Build a Windows Mobile application and submit it to the Marketplace for Windows Phones.   This post on the Windows Mobile team blog has more details.

Race to Market Challenge

• Prizes; 4 Microsoft Surface tables (Developer Edition), online marketing & promotion of your app and challenge trophies for the mantle.
• Applications will be judged on:
  • Most downloads of a free app
  • Most valuable app (downloads x price)
  • Most useful (as judged by Microsoft panel)
  • Most playful (as judged by Microsoft panel)
• Contest runs from launch to Dec 31, 2009.

The contest is open to ISV’s & Developers who live in countries or regions where Windows Marketplace for Mobile is available.  Further  details, including Official Rules, are available at http://mobilethisdeveloper.com.

Here are several blog posts to provide you the latest information on Windows Mobile and the Marketplace for Windows Phones:

http://blogs.msdn.com/robcamer/archive/tags/Windows+Mobile/default.aspx