Trying to decide which platform(s) to write your mobile app for?  Let me help you: iPhone.

Now, if you’ve got some extra time on your hands, you might build an Android version and hope at some point a better marketplace comes along and the rumored new Google-branded phone takes off.  Otherwise, stick to the platform almost half the US is using and has at least some discoverability mechanisms (Top category lists, New & Noteworthy, etc.).  As for RIM, Symbian, and Web OS…don’t bother.

Here are some numbers:

AdMob got significantly (17% vs 14%) more requests from Android users than they did Blackberry users in the US in September. [See Page 8]

As for worldwide:

  • iPhone is up to 43% (up from 33% in Feb and 40% in Sept)
  • Rim is down to 8% (from 10% in Feb)
  • Symbian is down to 29% (from 43% in Feb)
  • Android is up to 10% (from 2% in Feb)
  • Web OS is up to 5% (from 0% in Feb)

Summation: iPhone is kicking ass, Android has some momentum but is a long way away.  Taking into account iPhone’s domination and the number of Androids coming online, I wouldn’t put money on any other pony.