Can you expand on that statement? Why would a previous jailbreak mean you can't do the official unlock? Part of the official unlock is a full restore to factory settings isn't it?
I have a 3GS that AT&T say they have completed the unlock on, but when I go through the restore procedure it ends up at an error saying "There is no SIM installed". There is a SIM in it, and I've tried several SIMs all of which give the same error. Surely it doesn't have to be a current live AT&T account SIM to complete the process?
This is a phone that used to be on my AT&T account but when I upgraded to an iPhone 4 this was retired. I have used it as a jailbroken phone, but it is now on a fresh install of iOS5.
Trust AT&T to make the official unlock a long and confusing process even when they eventually give it to us....