Cant Activate Iphone. HELP!?

I had an iphone 3gs. Version 4.1. Jail-broken and unlocked. I recently restored it to factory reset via iTunes because i wanted to Un-jailbreak it. So it did all its resetting stuff. It seemed to go normal, it showed its language options then regional options... then it said connect to iTunes which it was already connected to. so the text changed itself to connected to iTunes. But on the iTunes screen on pc a message showed stating that the iphone could not be activated because it did not have a sim in.which it did (it had a GiffGaff sim inside) so i tried again, same message then i swapped the sim to o2, same thing happened. iPhone said connected to iTunes but stayed on that screen with the wire and iTunes logo whilst iTunes on pc stated it couldn't be activated. I also noticed in the top left corner where the carrier information usually is showed searching and after a few minutes showed no service. so it might be because its not unlocked to any carrier anymore which is why my sims didn't work. but i don't know who the original carrier sim was because the phone is second-hand and i don't have any contact information with the original owner. or is there another problem because im just speculating, i have no idea, and i'd rather not do hacker stuff.