ad 300x250 Microsofts ad platform now works with XNA developed apps for Windows Phone 7Developing for Windows Phone 7, want to make money off of your apps, but don’t want to charge for them or use Silverlight? Microsoft has heard your cries, and to assuage your requests now supports XNA applications with their advertising platform.

The Microsoft ad platform was formerly only functional with mobile applications created using Silverlight. If you are curious about the program itself you can find more information here.

There have been reports today from Windows Phone 7 developers that they are making more money off of free applications than paid applications in the Marketplace, something that Microsoft must already internally know. As we told you just an hour ago, sales data from the app store is weak thus far.

Will this cause a big spur in development for the platform? No, but it can’t hurt to have more options for more people. It’s the first rule of economics all over again, people respond to incentives, and so if Microsoft can create more revenue-positive reasons to write code for WP7, people will.

For now, we leave you with this question: at what point will the WP7 application store be ‘full,’ that is, when will it feel complete? 5,000 applications? 10,000?