Definition
A2P means Application to Person. It is to send SMS messages from software to personal mobile phones.
A2P SMS is used for business, therefore it is also called enterprise SMS or professional SMS.
A2P & P2P Difference
A2P: application to person. P2P: person to person.
A2P SMS is sent by SMS service platforms, while P2P SMS is sent by network carriers.
A2P SMS: sent number is long code, short code, or alpha sender ID based on the different regulations in different countries. P2P: sent number is a personal mobile phone number.
A2P SMS: for business use. P2P SMS: for personal use.
A2P SMS Use Cases
1. Promotions
A2P SMS is a convenient way to reach customers. Enterprises use it widely for promotion. Check up your phones, and you must have received many SMS messages from all kinds of merchants. A2P SMS is not new, and we're used to that.

2. Customer Service
If the enterprise gets a short code to send A2P SMS, it can receive inbound SMS from customers with keywords. The enterprise can reply with the pre-set messages from that short code.

3. Technical Support
Users can send keywords to the short code of the enterprise to get different services. For example, they can send "help" to trigger related services through SMS.

4. Notifications & Alerts
Financial companies and banks have been using A2P SMS to serve their clients for a long time. They send many notifications, like balance reminders, payment alerts, account status, etc.

5. Verification
Currently, 2FA (two factors authentication) is the most popular method to verify identity. It double-checks the validity of the account with a password and a verification code sent to your phone.

Ways to Send A2P SMS
Different countries have different regulations about A2P SMS sending. There are 4 types of numbers to send A2P SMS.
1. Long Code (10DLC)
A long code is a standard 10 digits number used for sending SMS and MMS messages. It is a fixed number like a human number.
2. Short Code
A short code is 5-6 digits number. It can receive inbound SMS to realize simple interactions. Also, the number is easy to remember, which is convenient for people to contact you.
3. Toll-Free Numbers (Only in the US)
According to Wikipedia, a toll-free telephone number or freephone number is a telephone number that is billed for all arriving calls instead of incurring charges to the originating telephone subscriber. For the calling party, a call to a toll-free number from a landline is free of charge.
Only in the US that toll-free numbers can send A2P SMS.
4. Alpha sender ID (In India)
For domestic transactional and domestic promotional (opted in) SMS, the sender ID must be 6 digit alpha (not alphanumeric) with preregistration in India.
While in other countries, there are different rules. You shall look into the local regulations. Or you can cooperate with an SMS provider so they can help you with that.
To know more about long code and short code, check this article: Long Code? Short Code?
A2P SMS Markets
According to Marketsandmarkets, the global A2P messaging market size is expected to grow from USD 62.1 billion in 2020 to USD 72.8 billion by 2025.
Due to Covid-19, the A2P SMS market has been growing even faster. More people are receiving information and communicating through mobile phones. And more businesses are reaching customers through phones.
