there been a report. You can try turn on/off air plan mode or turn off 3G and see what happen. Hope it help.

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Iphone 3G White!!
Filmware 2.1
Unlocked using I-smart sim
Text: In/Out <ok
Call: In/Out <ok
Signal: No service sometime
GPS: Work
Wifi: no problem
Dev Team and TA_Mobile(gsmvn) are the best team everrrr