Iphone 3g won't recognize sim card

[usm2561]

hi my iphone 3g won't recognize my sim card. It was recently jailbroken on v 2.1. I have ATT service, i was wondering if it is the phone or do i still need a unlock card like the gevey 3g?

[2056]

do you have another at&t phone to test the sim card in?
if not, try going to a local store to test another phone.

[usm2561]

It works perfectly in my Tilt but do i still need an unlock because i dont have an iphone sim card?