A2P, application-to-person, is messaging sent by software on behalf of a business to a consumer: appointment reminders, order updates, one-time passcodes, fraud alerts and marketing. It is the opposite of P2P, one person texting another from a handset. Nearly all business texting is A2P, and in the United States that classification decides what has to be registered before a message is allowed to send.
Why the label matters
The line is drawn by who is sending, not by what the message says. A support agent typing a reply in a shared inbox is still sending A2P, because an application transmits the message. US carriers treat unregistered A2P traffic from an ordinary 10-digit number as suspected spam and filter or block it, which is why A2P from local numbers must be registered through 10DLC, toll-free numbers must be verified, and short codes must be approved separately.
A2P over RCS
The same rules carry into RCS. A business sends RCS through a verified RBM agent, and wherever a phone cannot receive RCS the message falls back to SMS from the registered 10-digit number, so the 10DLC campaign has to exist and match the use case. Consent under the TCPA applies to A2P regardless of channel; how RCS consent works sets out what counts.
On SimplyRCS
Brand registration, campaign vetting and the RCS agent submission are filed for you, with registry fees passed through at cost from the rate card.