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Introduction

-AT commands are used to control a modem. AT is an abbreviation for Attention.
-Many of the AT commands used to control wired dial-up modems are also used for GSM/GPRS modems (cell phones). E.g. ATA,ATO,ATD,ATH.
-Besides these there are specific AT commands for GSM modems like for SMS i.e. AT+CMGS (Send SMS message), AT+CMSS (Send SMS message from storage), AT+CMGL (List SMS messages) and AT+CMGR (Read SMS messages) and are known as extended AT commands .
-Extended commands start with ‘+’ whereas basic donot