Eldar Murtazin, editor-in-chief of Russian mobile phone blog Mobile-Review, reports via Twitter that iOS 5 will not be compatible with the iPhone 3GS.
Just one comment. Apple iPhone 3Gs wont be upgradable to iOS 5.x. iPhone 4 will.
At this time, the statement is unverified. However, Apple is known to drop support for older models of iOS devices.
When Apple released iOS 4 in June 2010, the software was compatible with the iPhone 3G/3GS/4, but some of the features only worked in a limited capacity, or not at all, on the 3G/3GS.
Eventually Apple cut support for the iPhone 3G altogether, allowing users to update as far as iOS 4.2.1. With the next iPhone due this year, it seems that iPhone 3GS owner will have their updates capped at iOS 4.3.3.