Why won't iPhone activate after restore?

My iPhone 3GS was jail broken in order to unlock it so that it would work on T-mobile now that I'm no longer on Tmobile I did a factory restore in order to take off the jailbreak and unlock from the phone the problem is that when the resore is done it won't get past the activation screen. It says it can't activate even with an at&t sim card. I don't know what to do I don't wanna 'hactivate' it because that will be another jailbreak I want this phone to be back to normal-stock apple

Call apple support and they will activate the phone for you. Or take it to apple store if there's one near you.