Glossary

The telecom and verification terms behind our checks, explained with sources.

10DLC: 10DLC is US business text messaging sent from ordinary 10-digit phone numbers, registered by brand and campaign. How registration works and why it affects delivery.
A2P SMS: A2P SMS is text messaging sent by software on behalf of a business, such as one-time passcodes, alerts and reminders. How it differs from P2P and how it is regulated.
Caller ID name (CNAM): CNAM is the caller name shown with incoming calls in North America, looked up by the called party's carrier. How it works, why it is often wrong, and what we don't do.
Delivery receipt (DLR): A delivery receipt (DLR) is the status report a network returns after an SMS is delivered or fails. What DLR statuses mean and why a missing receipt isn't proof of failure.
E.164 phone number format: E.164 is the international phone number format: a plus sign, a country code and up to 15 digits in total. Why APIs use it and how to convert to it.
HLR lookup: An HLR lookup queries a mobile number's home network to find out whether the number is live, ported or roaming. How it works and what it can't tell you.
International mobile subscriber identity (IMSI): The IMSI is the permanent identifier of a mobile subscription, stored on the SIM. How it differs from the phone number and why MobileValidate never returns it.
International revenue share fraud (IRSF): IRSF is telecom fraud that pushes calls or texts to high-cost international numbers so the fraudster earns a share of the fee. How it works and how to limit it.
MCC and MNC codes: MCC and MNC codes identify a mobile network: a 3-digit country code plus a 2- or 3-digit network code, defined by ITU-T E.212. How to read them.
Mobile number portability (MNP): Mobile number portability lets subscribers keep their number when they switch networks. Why it breaks prefix-based carrier detection and how to handle it.
MSISDN: An MSISDN is the full international phone number of a mobile subscription: country code, network code and subscriber number. How it differs from the IMSI.
Number reachability: A valid number has the right format; a reachable number is live on a network right now. Four levels of phone number checks and what each tells you.
Phone number line type: Line type is the kind of service a number belongs to: mobile, fixed line, VoIP, toll-free, premium rate and more. What each means for SMS and calls.
Rich Communication Services (RCS): RCS is the carrier messaging standard that adds rich media, read receipts and verified business messages to the phone's built-in messaging app. How it differs from SMS.
Signalling System No. 7 (SS7): SS7 is the signalling protocol suite that phone networks use to set up calls, route SMS and support roaming. Why its trust model creates security risks for SMS codes.
SIM swap: A SIM swap moves a phone number to a new SIM. In SIM swap fraud, a criminal does it to receive the victim's calls and one-time passcodes. How it works and how to defend.
SMS pumping: SMS pumping is fraud in which bots trigger OTP or sign-up texts to numbers that earn the attacker a share of the fees. How it works and how to reduce it.
STIR/SHAKEN: STIR/SHAKEN is the caller ID authentication framework used in US and Canadian phone networks. How attestation levels A, B and C work and what they don't tell you.
VoIP number: A VoIP number is served over the internet, not a mobile or fixed network. Why it matters for OTP and fraud checks, and why it is not a red flag alone.
Wangiri: Wangiri is a phone scam: a call rings once from a high-cost international number to trick people into calling back. How it works and how businesses avoid paying for it.