can att&t or apple locate it based on it's serial number or something else maybe? Because when you plug it into iTunes, you catch the thing telling you the serial number. or could they at lowest possible tell me who is using the phone with a given serial number if the creature using it begins using the phone on another plan? and how can I find out the serial number of the iPhone I had that is to say now missing... does it save it on iTunes?
Answers: They can't "locate" it per articulate. Once you loose it, ask them to black list the IMEI number(like a serial number), which is inside the phone. Once the system finds out that someone is using that exact phone. they will be alerted and will try to contact that person.
As for finding the serial number, I really don't know.