Im new at this, I jailbroke my 3g 4.0.1 with redsnow and unlocked it with cydia using ultrasn0w, and my service always fluctuates from 1 bar to full bars to no service, my carrier is tmobile, i place a at&t sim in and it got full bars and 3g i placed other tmobile sims in and same issue, i know this has been a issue for other people as well but i havent seen a solution

For T-Mobile U.S you should turn 3G off as it is incompatible with iPhone's hardware.

The unlock itself is not causing poor service, it simply allows you to connect to other carriers.

Try turning off the 3g, that's my best advice... If it doesn't help, you should test another t-mobile phone to see if this one gets good service in the same area yours don't.



Rafael

Originally Posted by element

For T-Mobile U.S you should turn 3G off as it is incompatible with iPhone's hardware.

100% correct. Though both AT&T and T-Mobile advertise 3G, they use different radio frequencies. The iPhone is capable of roaming onto T-Mobile's 2G network as it uses the same frequencies as AT&T's 2G/EDGE network, but you cannot get 3G data service on the iPhone with T-Mobile presently.

When the 3G came out, there were rumblings that people were going to try and find alternate baseband chips or modify the crystal, etc., but none of that ever panned out -- so unfortunately T-Mobile's 3G is off-limits to the iPhone. You do need to disable it in the settings.app or your phone will say there is no service.