The "A2P" part matters, and it is the source of most confusion. A2P means an application is sending the message rather than a human typing it, which covers essentially all business texting: appointment reminders, order updates, one-time passcodes, marketing. "A2P 10DLC" and "10DLC" are used interchangeably in practice. Person-to-person texting from your own handset is unaffected and needs no registration.
Three parties are involved. You register. The Campaign Registry (TCR) is the central body that holds brand and campaign records and issues a trust score. The carriers, AT&T, Verizon, T-Mobile and others, read that record and decide your throughput and filtering treatment. Your messaging provider submits the paperwork on your behalf and passes through the registry fees at cost.
- 10DLC applies to A2P messages sent from standard 10-digit US numbers, not to toll-free or short codes, which have their own approval paths.
- Registration is per brand and per campaign, so a business running marketing and transactional programs registers each separately.
- Unregistered A2P traffic on a 10-digit number is heavily filtered or blocked outright, which is usually why "our texts stopped arriving" happens.
- SimplyRCS handles brand and campaign registration for you and passes carrier and registry fees through at cost.