By November 2007, the total number of mobile phone subscriptions in the world had reached 3.3 billion
...And they are all using windows mobile are they? LOL!. Dont forget almost all of those 3.3 billion cellphones are old bricks using whatever firmware crud comes with them. Phone, SMS, address book and calculator.
Hardly a comparison.
If Linux can't penetrate the PC market, what makes you think they're going to beat both Microsoft AND Google in the cell phone market?
Google would probably be swinging with some kind of linux.. Like they do now : http://en.wikipedia.org/wiki/Google_AndroidTheir server infrastructure is linux based too btw.