Every SMS on a US network is classified as either P2P (person-to-person) or A2P (application-to-person), and the two live under completely different rules. Misunderstanding the line, especially by believing that "conversational" texting from software counts as P2P, is one of the most common ways businesses end up filtered or blocked.
The definitions
P2P is a human with a handset (or handset-like app) texting another human: consumer-grade volume, balanced back-and-forth conversation, one number per person. Carrier rules of thumb for P2P look like a human: on the order of one message per second, a roughly balanced send/receive ratio, and messages to a small number of distinct recipients.
A2P is everything where software originates the message: bulk campaigns, yes, but also one-at-a-time messages triggered by an application: appointment reminders from scheduling software, order updates, OTP codes, CRM-sent sales follow-ups, and messages typed by an agent into a business texting platform.
The test is origination, not tone
The mistake businesses make is judging by content: "our messages are personal conversations with customers, so they’re P2P." Carriers judge by origination: if the message left an API, a CRM, or any software platform on behalf of a business, it is A2P, even if a human typed it, even if it goes to one recipient, even if the customer texted first.
In practice: texting from your personal phone’s native messaging app is P2P. Texting from anything you had to log into (Twilio-powered apps, sales engagement tools, support desks) is A2P and requires 10DLC registration (or a verified toll-free / short code route).
Will your website pass carrier review?
Paste your URL into our free AI scanner and get an instant PASS / WARN / FAIL compliance report. No signup needed.
Run a free compliance scanWhat each classification gets you
| P2P | A2P (registered) | |
|---|---|---|
| Registration | None | Brand + campaign via TCR |
| Throughput | Human-scale (~1 msg/sec) | Defined tiers, far higher |
| Filtering | Aggressive if volume looks automated | Sanctioned lane; content filtering still applies |
| Fees | Standard messaging rates | Registration fees + per-segment carrier surcharges |
Some platforms historically routed business traffic over "P2P" routes to dodge fees, a practice called grey routing. Carriers have systematically shut this down; grey-routed traffic today gets filtered quickly and can get numbers blocked entirely.
Why the distinction exists
Carriers built the A2P framework because unregulated software-driven traffic was drowning users in spam. The bargain of registration is real: registered A2P senders get deliverability that unregistered traffic never sees. The cost is accountability: a verified identity, declared use cases, documented consent, and adherence to content rules.
If you are reading this as a business, the conclusion is short: your traffic is A2P. The only real question is which registered route fits. For that, see our comparison of 10DLC, toll-free, and short codes.
Frequently asked questions
If my customer texts me first, is my reply P2P?
No. If your reply is sent from business software (a support desk, CRM, or texting platform), it is A2P regardless of who initiated the conversation. Inbound texts do, however, establish consent for the conversation.
Are OTP and 2FA codes A2P?
Yes, they are the canonical A2P use case: software-originated, high-volume, one-way. They require registration like any other A2P traffic and have a dedicated 10DLC use case category.
What is grey routing?
Sending business (A2P) traffic disguised over P2P routes to avoid registration and fees. Carriers actively detect and block it, and providers that enabled it have been shut down. It is not a viable strategy.