I can think of a major market: operating systems.

Phones aren't like cars, they are more like computers (and becoming more so).

I'd argue that phones are becoming a lot less like computers and more like cars. At least the iPhone as an example, phones are becoming more and more an information appliance, taken for granted to "just work."

They might be able to do a lot of the things that a "real" computer does but you don't have the power to treat them like regular computers. You can't easily put a new OS on them, write software for them without going through a central market place, etc. Apple obviously has this vision, but it's becoming clear that Microsoft shares it, at least for Windows Phone 7.

Right. People own a variety of computers. Different models of Dell, HP, sony, apple., etc.

Also known as: Windows, Windows, Windows, or OS X.

Or Intel, Intel, Intel ...

You can pick the abstraction level to suit the argument.

Not exact product, but same range of products: portable mp3 players.

What excatly is "same" between the teeny shuffle and an iPod touch? This only underscores my point that you need a fair amount of diversity in your products o dominated a market.