need help iphone 3g

[jdog]

i have an iphone 3g. i jailbroken it and also got a unlock sim chip from this web site: unlocked iphone. i have tmobile service with unlimited data plan. i have several problems i encountered. 1. i can not make outgoing calls the phone hangs up when i try to place the call then the tmobile signal fades and restores. 2. if i am in an area that does not get tmobile coverage my iphone says no service, but once i return to an area where there is tmobile coverage the phone still says no service so i have to take the tmobile sim card out of the iphone and insert it into a tmobile phone dail a number then access the internet then i can insert it into the iphone and it would reconize tmobile as the carrier. I Need Help