What is SMS (Short Message Service)?
SMS (Short Message Service) is a way to send short, 160-character text messages from one mobile device to another over the cellular telephone network. It is a public messaging medium that does not require registration with any third-party application, and is supported by almost all mobile phones in existence.
The networking technology and infrastructure behind SMS is largely abstracted away from end-users as most cell service providers (ie. mobile operators) offer the service as part of a mobile service plan or subscription package. All that is required to send or receive SMS is signal coverage from a nearby cell tower, which takes care of message routing and delivery using wireless communications standards such as GSM / CDMA / TDMA.
SMS was the most dominant form of texting on the planet until the proliferation of Internet-enabled smartphones, which granted users the ability to send and receive messages of any length, and of any data type, simply by installing an OTT messaging app like WhatsApp.
SMS still finds considerable business usage, however, since it is the only communication channel that is guaranteed to be present across different mobile phone models and brands. This makes it a particularly suitable channel for implementing Two-Factor Authentication since SMS is readily-available to anyone with a mobile phone.
The terms "P2P" (Person-to-Person) and "A2P" (Application-to-Person) are used to distinguish between the two main purposes of SMS. P2P describes ordinary SMS between two users, usually as part of a private conversation, whereas A2P entails any SMS sent programmatically from an application to the user.
A2P SMSes are typically sent on behalf of a company by a third-party SMS provider using SMS gateways and web-based APIs. Examples of A2P SMS usage includes direct marketing services (bulk SMS), online account notifications, alerts and reminders, and transaction confirmations.