Previous owner annoying problem iPhone 3G

Keep you cool they cannot read your messages nor what you are doing from what you said it sounds like the pervious owner jailbroke  the device before and locked his not information, not himself into the root your best bet is to buy another one because once information is embedded in the os it is very tedious to remove if you are not tech savy and willing to jailbreak to rectify this issue simply use the phone and save for the up coming iPhone 5 or i5 what ever their going to call it because it's never a good idea to buy an iPhone unless you bought it though an authorized dealer or a close family member or friend just a good word to the wise.

I did not man to include the not between his and information sorry.