So I have a jailbroken 4.0 with baseband 5.14.02.
It's not unlocked.
when I put 3 different at&t sim card it, it just says Searching... on the top left. Never a signal.
I tried restarting, network reset, and hard restart. No result.
Just wondering but why are you at 4.0 if you have 5.14.02 baseband? You may as well go to 4.1. If you are trying to use an official sim make sure you activate with itunes and not hacktivate with one of the jailbreaks.
Ya you can go to 4.1 but you will have to do it manually (save your SHSH with tiny umbrella while 4.1 is still being signed). If you restore to 4.2.1 you will not be able to jailbreak yet.
I have only ran into this prob once and it was when I tried to unlock a phone that couldn't be unlocked... Just uninstalled the unlock and it worked again