I have just uploaded my third app called Birthday Hub to the WP7 marketplace for review.
You can directly post to facebook, send an sms or email or make a phone call in this app. Just like in your contacts hub.
The design is a little oriented to the people hub.
The facebook integration is also necessary because it is not possible to directly read facebook birthdays from the contacts if there are some facebook contacts in it.
The trial version is a free version with no limitations but ads. The paid version has no ads.
If the app is certified and published to the marketplace i will it here.
I hope you will like Birthday Hub.
Here are some screenshots: