I jailbroke my 3gs about a month after i got it, was running fine, but then i noticed some numbers that had been dialled by my phone which i didn't do, it wasn't anyone using my phone as it was locked with a code, then random numbers like "77777###567886656" was dialed, now this looks like the phone had unlocked itself and dialed while it was in my pocket, but seeing as you have to slide to unlock it, then enter 4 numbers to unlock i found this impossible, so i restored it, and its run fine since. So i haven't a clue what happened.
Anyone else had the same?