GPRS shield V2.0 audio jack

im using GPRS shield V2.0 http://www.seeedstudio.com/wiki/GPRS_Shield_V2.0

I believe that 3.5mm four-connector TRRS standard earphone would work in the shield, but it seems that there is a problem in microphone connection in the shield. (I checked the microphone of my earphone using other device and it is working)

The speaker is working just fine with the shield when i tried to call someone via AT Command Tester V27 but the microphone doesnt. Is there a way to fix it or any alternative?.. i really need the mic. working with the shield. please help..