Embedded cellular modules are mainly controlled by the use of AT commands. AT or Attention Commands are derived from the Hayes Command set (or AT command set) from 1977 to control the 300-baud Hayes Smartmodem. They are a set of command-language or instructions that are sent to a cellular module to perform different actions.

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These commands or instructions can be sent over a USB, serial, or other interface to the cellular modules from the main controller of the application. Common AT commands include ATD to instruct the cellular module to make a phone call, AT+CMGS to send a SMS text message, and AT+GCACT to get an Internet Protocol (IP) address to start an IP data session.