A2P SMS

A2P (Application-to-Person) SMS is text messaging sent from a business application to a consumer phone — as opposed to P2P (Person-to-Person) SMS, which is regular human-to-human texting. A2P covers everything from package delivery alerts to bank fraud notifications to political campaign blasts.

How A2P routes differently

P2P traffic uses your phone’s subscriber identity (your phone number) and travels through the standard MO-MT (mobile-originated, mobile-terminated) SMS path. A2P traffic typically routes through specialized "messaging aggregators" (Twilio, Bandwidth, Sinch) that connect to the carriers via dedicated commercial channels:

• Short codes (5- or 6-digit numbers like 12345): pre-registered with carriers, vetted, premium pricing. Used for high-volume marketing or urgent alerts.
• 10DLC (10-Digit Long Codes): regular-looking phone numbers but registered with The Campaign Registry for A2P-rate routing. Standard for transactional SMS since 2021.
• Toll-free SMS: the 800/888/etc number range, also A2P-routable.

Why this matters for cell-plan users

Several user-facing things are downstream of A2P routing:

• 2FA codes that don’t arrive. Carrier spam filters sometimes mistake A2P 2FA codes for marketing. Major carriers maintain allowlists; new short codes can take days to propagate.
• Group messaging quirks. A2P short codes generally cannot receive group messages, only one-to-one. This is why business notifications never join your iMessage threads.
• iMessage vs SMS for businesses. Apple’s Business Chat is a separate channel; most businesses still send SMS (which renders as green bubbles) rather than iMessage (blue) on iOS.

For users on small Lifeline carriers or some MVNOs, A2P delivery can be less reliable than on the big-three postpaid — the carrier’s integration with The Campaign Registry and their spam filtering is what determines whether banks’ 2FA codes arrive.