A2P (application-to-person) messaging is traffic originated by an application, platform, or automation and delivered to a person’s handset. Appointment reminders, one-time passcodes, delivery alerts, and promotional SMS are A2P. P2P (person-to-person) is two people (or a small group of people) texting through native messaging apps. Carriers and CTIA treat those classes differently because A2P is high-volume, often one-to-many, and historically the source of spam and grey routes.
In the US, A2P over 10-digit numbers is 10DLC, A2P over 5- or 6-digit codes is short code, A2P over 8XX is Toll-free texting, and rich branded sessions may use RCS Business Messaging. The content layer is still SMS or MMS (or RCS). The registration layer is what tells the terminating wireless network that the traffic is declared A2P rather than disguised P2P.
A2P vs P2P vs P2A
| Class | Originator | Typical volume | US access path | Consent expectation |
|---|---|---|---|---|
| A2P (application-to-person) | An application, CPaaS, or campaign engine | One-to-many or high-rate one-to-one | 10DLC, Short codes, Toll-free texting, or RCS RBM | Use-case appropriate consent. Marketing: prior express written consent under TCPA. |
| P2P (person-to-person) | A human using a phone or consumer app | Conversational, low rate, mostly two-way | Native wireless SMS/MMS (and consumer RCS / iMessage) | Ordinary interpersonal communication. Pumping P2P to look like A2P is a grey route. |
| P2A (person-to-application) | A human texting a keyword or a chatbot number | Inbound to an application | The same long code, short code, or toll-free number the A2P program published | Keyword opt-in is one common proof of consent for the A2P replies that follow. |
Grey routes
A grey route is A2P delivered over a path that was priced or provisioned as P2P (SIM farms, international P2P interconnect, handset parks, or long codes that were never campaign-registered). Grey routes undercut declared A2P rates and evade SHAFT / consent checks. US and international wireless providers filter them: delivery receipts become unreliable, messages arrive late or not at all, and the numbers are eventually shut off. After 10DLC and the Unregistered Toll-Free sunset, grey long-code A2P into US handsets is a filtering problem, not a viable architecture.
- Declared A2P: registered campaign or verified sender, CTIA-aligned consent, billed on A2P rates.
- Grey route: P2P-priced path carrying application traffic. Unstable and against carrier codes of conduct.
- Blocked route: unsigned, SHAFT, or spam-signature traffic. DLRs may still say “sent.”