A2P (Application-to-Person) and P2P (Person-to-Person) are the two fundamental categories of SMS messaging, and understanding the difference matters for every business that sends text messages at scale. Carriers filter, route, and price these message types differently — and sending A2P traffic over P2P channels is one of the fastest ways to get your messages blocked or your sender ID blacklisted.
What Is A2P SMS?
A2P SMS refers to automated messages sent from a business application to a consumer’s phone. Examples include:
- Marketing promotions and flash sale alerts
- Two-factor authentication (2FA) codes
- Appointment reminders and booking confirmations
- Shipping notifications and delivery updates
- Account alerts and password resets
A2P messages travel through dedicated routes and are subject to carrier filtering, throughput limits, and compliance rules like 10DLC registration in the United States.
What Is P2P SMS?
P2P SMS refers to messages sent between individuals — a person texting another person from their phone. Carriers allocate more bandwidth and apply less filtering to P2P traffic because it represents normal consumer communication.
Why the Distinction Matters
Carrier Filtering
Carriers actively detect A2P traffic sent over P2P routes. If your business sends automated messages using personal phone numbers or unregistered long codes, carriers may throttle or block your messages entirely. Registration through programs like 10DLC (for long codes) or using short codes ensures your A2P traffic is properly routed.
Deliverability
A2P messages are only as good as the phone numbers they target. Sending to disconnected numbers, landlines, or VoIP numbers that don’t support SMS drives up failure rates and can damage your sender reputation with carriers and aggregators.
Cost
A2P messaging typically costs more per message than P2P. Every failed delivery to an invalid number is money wasted — and at scale, those failures compound quickly.
How Phone Validation Improves A2P Performance
Before sending any A2P message, validating the recipient’s phone number ensures:
- The number is mobile — Landlines and many VoIP numbers can’t receive SMS. Line type detection filters these out before you send.
- The number is active — Deactivated or suspended numbers silently consume your messaging budget without delivering.
- The carrier data is current — Ported numbers need to be routed to the correct network. Outdated carrier data leads to failed deliveries.
- The timezone is known — For marketing messages, sending at the right local time improves open rates and keeps you compliant with time-of-day regulations.
CheckThatPhone returns all of these fields — line type, carrier, deliverability, porting status, and timezone — in a single API call.
Best Practices for A2P SMS
- Register your sender — Use 10DLC registration for long codes or apply for a short code for high-volume campaigns.
- Validate before sending — Check every number for line type, deliverability, and carrier data before queueing a message.
- Respect opt-outs — Maintain suppression lists and honor STOP requests immediately.
- Time your messages — Use timezone data to send within appropriate local hours.
- Monitor delivery rates — Track failures by carrier and source to identify data quality issues early.
Getting Started
A2P SMS deliverability starts with clean data. By validating phone numbers before every send, you reduce failures, protect your sender reputation, and get more value from every message. Read the API documentation to integrate phone validation into your messaging pipeline, or explore pricing plans to start improving your A2P delivery rates today.