In a single Tweet Eldar Murtazin, editor-in-chief of Russian mobile phone blog Mobile-Review has cast speculation on whether the next major update to iOS will be compatible with the iPhone 3GS.
The tweet posted earlier today reads: "Just one comment. Apple iPhone 3Gs wont be upgradable to iOS 5.x. iPhone 4 will."
Naturally a tweet is very informal and is not attributed to any sources but Murtazin has a good reputation for mobile related rumours but not of the Apple kind.
When Apple released iOS 4 last June it was compatible with the iPhone 3G, 3GS and 4, support for the iPhone 3G was dropped earlier this year with the release of iOS 4.3.