iPhone randomly won't detect sim card. (Unlocked)

[xDeathReaperx]

My iPhone is having a hard time detecting an unactivated AT&T sim that I used just to get pass the home screen. It worked twice in the past hour then it just randomly says "NO SIM CARD". I unlocked the iPhone 3g 4.2.1 now w/ iPad baseband and it will NOT detect my T-Mobile Sim Card..

HELP!?

 

[PsstGreek]

Make sure you have 3G off. Also that ultrasn0w is installed through Cydia.

 

[xDeathReaperx]

Make sure you have 3G off. Also that ultrasn0w is installed through Cydia.

I turned it off, and it still won't detect neither sim card.

Also; should it give me an option to choose my network? Because it doesn't...

HELP!!!!!!!!!!!!!

 

[xDeathReaperx]

YES!!! I got it to work following this video: http://www.youtube.com/watch?v=0RJTZqeO0Cs