My iphone 3gs will not read sim?

Won't read sim cards stuck on activation Screen

so i have this iphone 3gs. And it was jail broken and unlocked a few years ago. It was last on 4.1 and base-band 6.15.00.so i heard that apple was now allowing unlocks so i requested it to be unlocked. They said they unlocked it just got to restore it through itunes.well i did this and now its at the activation screen. I have an active att sim and when i try to activate it it says that there's an error and itunes says need to put sim in. But the sim is already in. So i'm assuming its not readying sim cards. And since it is stuck on activation screen i can't even axcess the information on the phone. Accessdvice would be helpful.

You must downgrade that baseband by downloading the latest RedSn0w 0.9.14b2 or newer.
Here are the downgrade instructions:
http://www.redmondpie.com/how-to-downgrade-iphone-3gs-3g-06.15.00-to-05.13.04-baseband-for-unlock-and-working-gps/