When the iPhone 5 arrives, will the iPhone 3GS become obsolete?

I am planning on buying an iPhone, but do not want to spend the big bucks on an iPhone 4. The logical solution for me was to purchase the iPhone 3GS. However, I recently heard rumors of the iPhone 5's arrival. When the iPhone 5 does come out, will I still be able to purchase software, apps, accessories such as cases, etc. for the 3GS? Please understand, buying the iPhone 4 or 5 is NOT an option for me.