A2P 10DLC stands for Application-to-Person Application-to-Person 10-Digit Long Code messaging — the registered framework US carriers use for business SMS sent from regular 10-digit phone numbers (as opposed to short codes or toll-free).
Since February 2025, US wireless carriers (AT&T, T-Mobile, Verizon) require all business-volume SMS senders to register their brand and campaigns under A2P 10DLC. Unregistered messages from VoIP and standard business numbers are increasingly carrier-blocked — at filtering rates approaching 100% in 2026.
For business phone customers, this means SMS only works if the provider has handled brand and campaign registration with The Campaign Registry (TCR), the central A2P 10DLC database. Kelir registers brands and pre-approves typical small-business campaigns (transactional, customer notifications, appointment reminders) so SMS Just Works for customers without manual TCR submissions.