There are already tons of app that can do this. For e.g. Birthday Diary, the free app lets you view and manage friend's birthdays. Have a look at this, and many more apps, and then decide to do your new app.
And on the positive note, you should visit http://facebooktoolkit.codeplex.com/ . This is the codeplex version of the toolkit, and there is lots of goodies and information here. For a windows phone 7 sample, look at
Hope this information suffices.