if a jailbroken iPhone can be restored apple / att that it has never been jailbroken?

Currently, I'm having some problems with my internet. I dropped my iphone twice so far … once in a rubber case drive (which for a minute that my iphone sim not display a messege on the top left where the bar should be) and once when he was in my dlo leather pocket (do not think there was damage to it). And for 3 or 4 days now, even if my 3g iphone detects wifi or my AIM doesn't connect. He always says he needs a network connection. Even with my Cydia and Installer (jailbreak programs). So I want to know if I should restore my iphone and return it to the apple / att to repair, do they know so I jailbroke voiding warranty

if you restore it, they will not know

Piel Frama iPhone 3GS Leather Case Review by mrgadget.com.au