Long Zheng keeps digging into the latest Windows Phone 7 build being shown around at TechEd 2010. This time we’re seeing the new trial program API that developers can use in order to offer free trial versions of their programs in the Marketplace. The API is very simple, allowing a developer to offer a free trial that lasts however long they want, or it can have reduced functionality, or advertisements. It’s all up to the developer. Then, right within the app, if you as a user feel like upgrading to the full version, it’s no problem. You can do it right there. There’s no need to download a different version or even go back to the Marketplace.