I have got an i phone which is unlocked and jailbroken although when i put my vodafone sim in (or any other for that matter)....it showed no service....I then restored the i phone which locked it again although when i tried it with the original O2 sim it still showed no service....can someone tell me what the problem is and how to resolve it.
Does your O2 SIM work in another phone?
If your iPhone came wit that O2 SIM, and the SIM works in another phone and no longer works in your iPhone -- and you've restored the firmware with iTunes -- then it's a hardware problem.
Did you drop the phone between now and the last time you placed a phone call? If so, you can try taking it apart and seeing if anything came disconnected. Otherwise, the baseband is bad, and you will have to replace the main logic board to fix it -- see this guide for more information, but you're probably better off selling it for parts and buying a used phone on eBay.