P2P SMS

Person-to-person SMS: ordinary texting between two individual subscribers.

P2P (person-to-person) is classic texting between two phones. Carriers treat it as consumer traffic with consumer pricing and few registration requirements.

The A2P/P2P distinction matters commercially: sending application traffic over P2P routes ("gray routes") is cheaper but against carrier rules, and messages on such routes are filtered more aggressively, which is one reason some verification codes never arrive.