The GSM Shield V2 library has new audio commands suitable for voice calls and position command. Audio commands allow to set audio channel, ringer sound level, speaker sound level, speaker loudness, speaker mode, alert sound mode, loud speaker volume level, mute control and microphone gain level. Position command retrieves longitude and latitude. To use these functions you have to declare a new object type, this type is GSM2. The following fragment of code explains how.
Note: the GSM2 is integrated into GSM library and it is already available in the Arduino IDE. You can download it here