The iPhone is riding the popularity wave and hasn't fallen off yet. Right now the idea of something "stopping" it is not possible. It will simply need to run its course.
However, what the market really needs right now is a low-cost alternative to the iPhone, that features robust support for a lot of common enterprise tools such as Outlook/Exchange/Sharepoint, and has a more open development environment (which allows for services).
Google's various comparable offerings keep losing the low-cost part with their most recent one weighing in at $400+ IIRC. Microsoft has the skill and the software base to make a very competitive product that, while not stopping the iPhone, would change the landscape of the market.







