My iPhone is activated with AT&T so no need to jailbreak on my end.

However, I did the steps anyways because I will be switching over to T-Mobile soon.

My steps... I downgraded to 1.11 and jailbreak and oktoprep. Updated to 1.1.2 and jailbreak with 1.1.2 jailbreak zip. I installed BSD and the iClarified Gui unlock. Unlocking process went fine and the phone rebooted. Popped in T-Mobile sim and I get the different sim error. Of course my AT&T sim works perfectly.

So is it just a problem for those who already have an activated phone?