Yes, hacktivation screws a lot of things up.
Here's a trick, directly from Geohot - if you still have your AT&T SIM card - EVEN IF ITS NOT ACTIVE - you can insert that when you restore to activate your iPhone. But it will only work on the 3G, so yore lucky. After you activate, insert your carriers SIM card and reboot your iPhone.
But when you restore, as another poster said, restore your iPhone and set it up as new. Don't Restore from backup.