GSM modules are often used in high altitude ballooning as a backup telemetry system. Due to the horziontal plane in which GSM networks are setup (to maximise reception on the ground) GSM doesn't work above approximately 2km altitude. If the module tries to send a SMS it just times out when the module is above the max altitude. On returning back down to below 2km the module is able to get a connection and can then start sending messages again.

There are a number of methods available to connect GSM modules to your flight computer to act as another form of communication.