The upcoming iOS 5 will not be compatible for iPhone 3GS and previous versions. Well, this is just a rumour but I personally feel that it will be true. Two reasons for this :
– pure marketing strategy. Who don’t want a profit? Apple must stop updates for iPhone 3GS so that the users of this model will eventually upgrade their phone, hopefully to another latest iPhone. Anyway, I appreciate that Apple was providing support for a model which is already deemed outdated. Some other manufacturers and OS makers will not even be bothered about their “older” models after few months.
Again, nothing is finalised. Let’s see what Apple has got to say.[SOURCE]