iPhone 3GS unlocked cannot find network please help!

[RedBaron589]

Iphone 3GS old version
Firmware:4.2.1
Modem Fireware:5.15.04


Recently jailbroke (untethered) and unlocked my iPhone 3GS, I have been dealing with this for the last few days trying to use T-Mobile prepaid sim card in my AT&T phone. I used redsnow 0.9.06b6 and iPhone2,1_4.2.1_8C148a_Restore.ipsw which I restored to through itunes. After I restored my phone to the custom firmware I used the redsnow to jailbreak it, everything worked fine. I got to the unlock portion through Cydia did that and the phone rebooted just like it was supposed to everything looked fine but for some reason my phone wont find a network not with any of the 3 T-mobile prepaid sim cards it either just keeps searching or says no service, I try to access the carrier settings but it says its not availible also i noticed it reconizes the sim card because it shows up and the about info as TeleKom which is the German network that I'm using (which is Tmobile). Not sure if i missed something if anyone knows a fix please help.

[Supra1jz]

5.15.04 cannot be unlocked you need to be on 5.13.04 or less and on iphone 4 1.59

[Stray]

You can update to the iPad baseband.