The iPhone is already cheep. You can get one for $99.
The problem with anyone competing with iPhone, is the same problem with anyone competing with Apple as a whole. Only Apple (in the computer industry), measures the right metrics for success. Apple cares about how a device effects your life, not what the device is (why you never hear about specs much from Apple).
A very early example of this was Fugi with camera design. Back in the 70's, every camera company was looking to make a camera with the best features. They wanted the best lenses, options, bodies, etc...
Fugi looked at what people wanted out of a camera... better pictures. The pictures is what mattered to the users, and not the camera itself. So, Fugi built and marketed cameras that made it easy to take better photos (auto focus, auto feed film that would not get exposed, automatic settings... etc).
This way of thinking exploded Fugi's market (they are currently the world’s largest photographic and imaging company), and they never looked back.
Microsoft has the money and capability to take down the iPhone. They just have never had, and probably never will have, the mindset needed.







