Sixty terms you will meet while buying phone numbers, registering for 10DLC, setting up SIP trunks or reading a carrier rejection notice, each explained in plain English in about a hundred words. Where a term deserves more than a paragraph, the entry links to the full guide. Type in the box to filter, or jump by letter.
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Ten-digit long code: an ordinary US local phone number that has been registered for application-to-person (A2P) messaging. Since the US carriers made registration mandatory, every business text sent from a local number must belong to a registered brand and campaign at The Campaign Registry, and the brand's trust score sets how many messages per minute the carriers accept. Unregistered local-number traffic is filtered or blocked. Start with the complete 10DLC registration guide or run the readiness checker.
A login that needs two independent proofs: something the user knows (a password) and something they have (a phone that receives a one-time passcode, or an authenticator app). SMS and voice OTPs remain the most widely deployed second factor because they work on every phone with no app to install. See OTP and the OTP SMS API.
Application-to-person: messages generated by software and sent to people, such as appointment reminders, delivery alerts, one-time passcodes and marketing texts. The opposite is P2P, a conversation between two humans. US carriers treat all A2P traffic as commercial and require it to run on registered routes: 10DLC for local numbers, verified toll-free numbers, or short codes.
The confidence level a voice provider stamps on a call under STIR/SHAKEN. Full attestation (A) means the provider knows the customer and confirms they are entitled to use the caller ID; partial (B) means the customer is known but the number is not verified; gateway (C) means the call merely entered the network from elsewhere. Lower attestation makes a call more likely to be labelled spam or blocked.
Showing a business name, and on supporting handsets a logo and call reason, on the recipient's screen instead of a bare number or a "Scam Likely" label. It is delivered through a mix of CNAM records, carrier branded-calling programmes and STIR/SHAKEN-verified identity. See CNAM and branded caller ID.
The first step of 10DLC: creating a record of your legal business at The Campaign Registry with the exact legal name, EIN, registered address, website, vertical and a contact. The brand is then vetted and scored. Because the record is checked against IRS and state filings, small mismatches in name or address are the most common reason a registration stalls.
Connecting your own telecom carrier to a cloud phone system or contact-centre platform over SIP trunks, instead of using the carrier the platform bundles. Businesses do it to keep their numbers and rates, to meet a regional compliance requirement, or because the bundled carrier's per-minute price is uncompetitive at volume. See SIP trunking.
A registered description of one messaging programme under a brand: its use case (customer care, 2FA, marketing, mixed and so on), a plain-language description, how people opt in, sample messages and how STOP and HELP are handled. Phone numbers are attached to a campaign, and what you send must keep matching what the campaign declared. The campaign approval checklist lists what reviewers look for.
Automated systems at the mobile carriers and their aggregators that delay, silently drop or reject messages judged to be spam or non-compliant. Filters look at registration status, sender reputation, content patterns (public link shorteners, missing opt-out language, restricted categories), sudden volume spikes and complaint rates. A message can be "sent" from your side and never reach the handset because of filtering, which is why delivery receipts matter.
A cloud-hosted contact-centre platform (queues, IVR, agent desktop, recording, analytics) sold as a subscription instead of installed hardware. Many CCaaS platforms let customers plug in their own carrier for voice through BYOC.
The name, up to 15 characters, displayed next to a caller's number on many US landline and mobile phones. It is not sent with the call; the receiving carrier looks it up ("dips") in a CNAM database at ring time. Getting your business name to display reliably means registering the name against your numbers and keeping the CNAM databases updated. See CNAM and branded caller ID.
The compression scheme used to carry voice on a VoIP call. G.711 is uncompressed, about 64 kbps each way, and sounds like a traditional landline; G.729 squeezes the same call to about 8 kbps at some cost to quality; Opus adapts its bit-rate and is common in browser-based calling. Both ends of a SIP call must agree on a codec, which is why codec mismatches show up as one-way audio or failed calls.
A message longer than one SMS, split into segments that carry a small header so the handset can reassemble them in order. The header costs space: each part holds 153 GSM-7 characters instead of 160, or 67 instead of 70 in UCS-2. You are billed per segment, and carriers may deliver the parts seconds apart. Check any draft in the SMS character counter.
A cloud platform that exposes telecom capabilities (SMS, MMS, RCS, voice calls, phone numbers, verification) as APIs so developers can build them into their own software rather than run telecom infrastructure. Signalmash is a CPaaS provider; so are Twilio, Telnyx, Bandwidth and Sinch. The differentiators are usually carrier relationships, compliance handling and price at volume.
The trade association of the US wireless industry. Its Messaging Principles and Best Practices document is the de facto rulebook the carriers enforce for A2P messaging: consent, opt-out handling, restricted content, sender identification and the expectation that a privacy policy does not share phone numbers with third parties. It is guidance rather than law, but a message that breaks it gets filtered all the same.
Originally a block of numbers a carrier routes straight to extensions on a PBX over a single trunk, so callers reach a desk without an operator. In CPaaS usage the term has broadened to mean any phone number provisioned on a platform, which is why API endpoints for buying and listing numbers are often named after DIDs.
The carrier's report that a message reached the handset, or failed with a reason. It arrives asynchronously, usually to a webhook, seconds to minutes after the send. A successful API response only means the platform accepted the message; the DLR is the record of delivery, and delivered-versus-sent ratios per carrier are the first place to look when filtering starts.
The National Do Not Call Registry run by the FTC, plus several state registries, listing numbers that must not receive telemarketing calls or texts without the consumer's consent or an existing business relationship. Lists must be scrubbed regularly and internal opt-out requests honoured. See DNC compliance for businesses.
The international standard for writing phone numbers: a plus sign, the country code, then the national number, with no spaces or punctuation and at most 15 digits, for example +15035550100. APIs and databases should store numbers in E.164 so that a US number, a UK number and a Canadian number sort, match and route correctly.
Employer Identification Number, the nine-digit tax ID the IRS issues to a US business. 10DLC brand registration checks the legal name you enter against the EIN record, so the name must match the IRS letter character for character, including "Inc." or "LLC". Sole proprietors without an EIN use a separate, more limited registration path.
The seven-bit character set used for standard SMS. It covers basic Latin letters, digits, common punctuation and a handful of accented characters and symbols, and allows 160 characters in a single message. A few characters in its extension table (the euro sign, curly braces, square brackets, backslash, tilde, caret and pipe) cost two characters each. Anything outside the set, including emoji and smart quotes, forces the whole message into UCS-2.
A reply of HELP to a business number must return an automatic message with the brand name, a support contact and how to opt out. Carriers and campaign reviewers check that it works. Sending it from the same number that sent the original message, within seconds, is part of the standard 10DLC and short-code compliance checks.
Verification of a business's identity and legitimacy before a provider issues phone numbers, messaging routes or voice trunks. In telecom it is driven by carrier rules and FCC robocall obligations rather than banking law, and typically involves confirming the legal entity, its website, its address and who is authorised to act for it. Expect it at sign-up with every reputable CPaaS provider.
A standard ten-digit phone number, local or toll-free, as opposed to a five- or six-digit short code. Long codes can carry voice as well as text, cost little, and look like a normal number to the recipient. Local long codes used for business messaging are what 10DLC registers; toll-free long codes go through toll-free verification instead.
The right, and the process, to move a phone number from one carrier to another and keep it. A port needs a letter of authorisation, the current carrier's account details and a billing record that matches exactly; mismatches are the usual cause of rejection. Simple US ports take days, complex ones weeks. See the guide to US numbering and portability.
A ten-digit number that identifies the switch currently serving a ported phone number. Because the dialled number no longer tells you which carrier owns it, the network looks up the LRN in the number-portability database and routes the call to that switch instead. LRN lookups are also how number intelligence services tell you a number's real current carrier.
Multimedia Messaging Service: the extension of SMS that carries images, audio, video and longer text. MMS is billed per message rather than per segment, so a long text with a picture can be cheaper than the same text as five SMS segments. Size limits vary by carrier, so media should be compressed before sending. In the Signalmash API an MMS is simply a message with an attachment; see the SMS API.
Throughput measures. AT&T assigns 10DLC brands a per-minute class based on trust score, from 75 messages per minute for unvetted low-volume brands to roughly 4,500 per minute at the top tier; T-Mobile applies a daily cap per brand instead. Short codes deliver hundreds of messages per second. Adding phone numbers does not raise a brand-level limit. Details in throughput and trust scores.
The shared numbering plan under country code +1 covering the United States, Canada and about twenty Caribbean and Atlantic territories. Numbers follow the pattern NPA-NXX-XXXX: a three-digit area code, a three-digit exchange and a four-digit line. It is administered by the NANP Administrator, which assigns area codes and number blocks to carriers.
The first two parts of a North American number. NPA (numbering plan area) is the area code; NXX is the central-office or exchange code, historically tied to a specific switch and rate centre. Together they determine which rate centre a number belongs to, which in turn decides whether a call is local and where a new number can be ordered from.
Assigning numbers to carriers in blocks of one thousand rather than ten thousand, so that a rate centre's numbers are not exhausted by carriers holding blocks they barely use. In messaging the phrase is also used loosely for a set of numbers that one campaign sends from; carriers dislike high-volume senders spreading identical content across many pooled numbers, a pattern known as snowshoeing.
A person's documented agreement to receive messages from a specific brand. Acceptable mechanisms include a web form with an SMS disclosure beside the phone field, a keyword texted to your number, a paper form, a verbal script or an in-app checkbox. Consent must be single-brand and cannot be a condition of purchase, and you should be able to show a screenshot of the opt-in for any campaign you register.
A recipient's instruction to stop. STOP, END, CANCEL, UNSUBSCRIBE and QUIT must be processed automatically and immediately, confirmed with one final message, and applied across the brand rather than one campaign. Continuing to message an opted-out number is the fastest route to TCPA liability and carrier suspension.
Carrier terms for the two directions of a voice call. Origination is receiving calls from the public network onto your numbers (inbound); termination is delivering your outbound calls to their destination on the public network. They are priced and provisioned separately, which is why a SIP-trunking quote lists inbound and outbound rates, and why toll-free origination is its own product.
A short numeric code sent by SMS or read out by a voice call, valid for one login or transaction and for a limited time, typically thirty seconds to a few minutes. A good OTP service generates and expires the code for you, ties it to a session and verifies the user's input, so the code never lives in your own database. See the OTP SMS API and Signalmash Verifier.
Person-to-person: a human texting another human from a handset, at human speed and volume. Carriers exempt genuine P2P traffic from A2P registration, but the test is behaviour, not intent: software sending one message to many numbers, or one number sending hundreds of texts an hour, is A2P however conversational the wording, and will be filtered if it is not registered.
The phone system inside a business that switches calls between internal extensions and the outside world. Modern PBXs are software (on-premises or hosted) and reach the public network over SIP trunks rather than physical phone lines; the number of concurrent outside calls the trunk allows is its channel count.
The global, carrier-operated telephone network that every ordinary phone number lives on. VoIP systems still need a gateway to it to call or be called by the outside world, which is exactly what SIP trunking and CPaaS voice products provide.
A geographic area, usually a town or part of a city, that carriers use to assign numbers and decide what counts as a local call. Every NPA-NXX belongs to one rate centre. When you search for a "local" number by city, you are really searching by rate centre, and a rate centre with no free blocks means no new numbers there until a carrier opens one.
Google's programme for brands to send RCS messages: a verified sender name and logo, rich cards, carousels, suggested replies and read receipts, delivered through Google-approved partners after the brand's sender identity is checked. It is the business half of RCS, the way short codes and 10DLC are the business half of SMS. See SimplyRCS.
The carrier-standard successor to SMS, built into Google Messages on Android and supported on iPhone since iOS 18. It adds typing indicators, read receipts, high-resolution media, group chat and, for businesses, verified sender branding and interactive cards inside the default messaging app. Messages fall back to SMS when the recipient's device or carrier does not support RCS. Read what RCS business messaging is.
The FCC requirement that every voice provider carrying calls to US numbers has a written plan for preventing illegal robocalls, files it in the Robocall Mitigation Database and implements STIR/SHAKEN where able. Calls from providers absent from the database must be blocked by downstream carriers, which is why a provider's filing status affects whether your calls complete. See US telecom regulations.
The unit an SMS is billed in. One segment holds 160 GSM-7 characters or 70 UCS-2 characters; once a message exceeds that it is split, and each part holds only 153 or 67 because of the reassembly header. A 161-character message is two segments and twice the price. The character counter shows the segment count and the character that tipped a message into Unicode.
Sex, hate, alcohol, firearms and tobacco: the content categories the US carriers restrict or prohibit on A2P messaging under the CTIA guidelines. Cannabis and CBD, gambling, high-risk financial products, debt relief, lead generation and affiliate marketing are commonly treated the same way. Some categories can be sent with age-gating and a special campaign type; others are refused outright regardless of the rest of the submission.
A five- or six-digit number leased specifically for high-volume A2P messaging. Short codes deliver hundreds of messages per second with no brand-level daily cap, are pre-approved by every carrier, and are the standard for large marketing programmes and two-factor traffic at scale. The trade-offs are cost, typically hundreds of dollars a month for a dedicated code, and an approval process measured in weeks. See short code messaging.
The signalling protocol that sets up, modifies and ends calls over IP networks: who is calling whom, which codecs to use, when to ring and when to hang up. The audio itself travels separately over RTP. Almost every VoIP phone, PBX and contact-centre platform speaks SIP, which is what makes trunks from different carriers interchangeable.
Connecting a PBX or contact centre to the public telephone network over the internet using SIP, in place of physical PRI or analogue lines. Capacity is sold in concurrent call channels, pricing is per channel plus per-minute usage, and one trunk can carry numbers from many locations. It is the usual way a business keeps its own phone system while cutting carrier cost. See SIP trunking from Signalmash and the SIP trunking pricing guide.
The original text-message standard, carried on the signalling channels of every mobile network and readable on every phone ever made. Its limits, 160 GSM-7 characters per segment and no media, are the reason concatenation, MMS and RCS exist. It remains the most reliable channel for time-sensitive messages because it needs no data connection and no app. See business text messaging.
Short Message Peer-to-Peer, the binary protocol carriers and aggregators use to exchange SMS in bulk over persistent connections. It is faster and leaner than HTTP for very high volumes but harder to integrate and debug, so most businesses use a provider's HTTP API and let the provider speak SMPP to the carriers.
The caller-ID authentication framework the FCC requires of US voice providers. The originating provider digitally signs each call with an attestation level; the terminating provider verifies the signature and uses it, with analytics, to decide whether to label or block the call. It does not stop spoofing by itself, but unsigned or gateway-attested calls are far more likely to show as spam.
The universal opt-out command. A reply of STOP (and its equivalents END, CANCEL, UNSUBSCRIBE, QUIT) must halt messages to that number immediately, trigger a single confirmation, and be recorded so the number is never messaged again without a fresh opt-in. Including "Reply STOP to opt out" in messages is expected by carriers and reviewers. See opt-out.
The 1991 US federal law governing automated calls and texts. It requires prior express consent for autodialled or prerecorded calls and texts to mobile numbers, prior express written consent for marketing, honouring of opt-outs and Do Not Call lists, and calling-hour limits. Statutory damages run $500 to $1,500 per message, and it is enforced largely through private lawsuits and class actions. Read the TCPA compliance guide for 2026.
The central registry, operated on behalf of the US mobile carriers, where 10DLC brands and campaigns are registered, vetted and given a trust score. Businesses rarely deal with it directly; their messaging provider (a "campaign service provider") submits and manages the records. Registry fees for brand registration, vetting and monthly campaign charges are passed through to the sender. See A2P 10DLC registration requirements.
Sending texts from an 8XX number. Toll-free numbers are not registered through 10DLC; instead the number goes through toll-free verification, a review of the business, use case, opt-in and sample messages that typically takes about a week. Verified toll-free numbers offer higher throughput than most 10DLC tiers and work across the US and Canada, which makes them a common choice for customer-support and notification traffic. See toll-free messaging.
A 0 to 100 score assigned to a 10DLC brand by The Campaign Registry's vetting partner, based on the company's public records, age, size and online footprint. Carriers map it to throughput: AT&T to a messages-per-minute class, T-Mobile to a daily cap. It is not a pass or fail, but a low score can make a legitimate programme unusable, and standard or enhanced vetting is the way to raise it. See throughput and trust scores.
Cloud-hosted business phone, video meetings, chat and presence sold as one subscription per user, replacing an on-premises PBX. Many UCaaS platforms let a business connect its own carrier through BYOC SIP trunks, keeping numbers and rates while using the platform's software. See the UCaaS provider comparison.
The 16-bit encoding an SMS switches to when it contains any character outside GSM-7: emoji, most accented letters, curly quotes, em dashes, non-Latin scripts. Every character then costs two bytes, so a single message holds 70 characters and each concatenated segment 67. One stray smart quote pasted from a document can double the cost of a campaign, which is what the character counter is for.
The third-party review of a registered 10DLC brand that produces its trust score. Standard vetting is an automated check of public business records and is the normal choice; enhanced vetting is a deeper, more expensive review that can unlock the highest throughput tiers. Skipping vetting leaves a brand on conservative default limits. Political, charity and some other special use cases require additional external vetting.
Carrying phone calls as data packets over IP networks rather than dedicated circuits. It underpins every cloud phone system, contact-centre platform and SIP trunk. Call quality depends on the network path (latency, jitter and packet loss) and the codec, which is why VoIP deployments prioritise voice traffic and monitor those three numbers.
An HTTP request the provider makes to a URL you supply whenever something happens: an inbound message, a delivery receipt, a call event. It is how your application learns about replies and delivery without polling. Your endpoint should respond quickly, verify the request came from the provider, and treat duplicate deliveries as possible. In the Signalmash API a webhook is registered with a single call; see the SMS API.
Tell us which word you hit in a carrier email, a contract or a rejection notice and we will add it, with the plain-English version. And if the term you were looking up is standing between you and a working messaging programme, the fastest fix is a conversation.
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