Why it`s over heating?
i found somthing but not workin`
Revamped version of the iPhone 3G with faster processing speeds. Repair of this device is similar to the 3G, and requires simple screwdrivers and prying tools. Model A1303 / 16 or 32 GB capacity / black or white plastic back.
iPhone's tend to overheat when you are doing 'heavy duty' activities. Try closing all of your applications (double tap home button to see open apps, if you have iOS 6 tap and hold on an app to show the 'x' symbol then press the symbol to quit the app. If you have iOS 7 then just slide each 'app preview' up). Also if you have a lot of applications using location services it may be the reason for why your phone is over heating. Try to minimize those as well.