Apple's new operating system is reportedly causing problems for both older versions of the iPhone.
Apple Inc.'s own support forum has been piling up with complaints from users that their iPhone 3G, which rolled out two years ago, is experiencing slowness, a quickly draining battery and overheating. The problems surface after the devices are updated with Apple's iOS 4 software, users say.
Similar complaints from iPhone 3GS users have been reported in Apple's discussion forums and various blogs since iOS 4 debuted in June.
Apple did not return phone calls or e-mails for comment.
Apple rolled out iOS 4 in June alongside the iPhone 4. Apple said that the operating system was compatible with iPhone 3GS and iPhone 3G models and that users should upgrade their devices with the new software.
On Monday, the Cupertino, Calif.-based company said it was investigating the complaints from users of the iPhone 3G but did not mention the iPhone 3GS.