I have tried a lot to connect Seeeduino Mega2560 and GPRS shield 1.2 but it does not work. AT Command Tester & Sscom is not responding. I have followed each and every instruction from the wiki. but nothing. Arduino 1.0.4 has GSM library. I have tried that codes. I have change the RX TX (7,8) to (10, 11) but nothing 
. Please give details instruction regarding this issue.
If you want to use GPRS shield with Mega,you need to modify two points:
1)Program:SoftwareSerial GPRS(7,8)----SoftwareSerial GPRS(10,11);
2)You need connect pin-7 to pin-10(pin-8 to pin-11) by jumper wire.Because of not all pins on the Mega and Mega 2560 support change interrupts.
Have a try!