iPhone 3GS Stuck on "Searching..." after jailbreak (5.1)

[crazyrockstar79]

I have an iPhone 3GS (jailbroken with RedSn0w 0.9.10b6(iOS 5.1 with iPad baseband 6.15.00). When I insert the AT&T SIM card, it sticks on "Searching..." or "No Service" What do I do??? Please help!

 

[Thierry ba]

Install Ultrasn0w from Cydia.

 

[destroyed92]

Guess ur baseband is locked..
U need to jailbreak ur device again and install a custom firmware...