BirdieSync cannot synchronize Windows Phone devices for several reasons.
When switching from Windows Mobile 6.5 to Windows Phone 7, Microsoft has introduced huge technology changes in its new operating system. A new layer has been added above Windows Mobile and developers can no longer access to Windows Mobile. But this new layer is very young, lacks a lot of technologies for developers and is far more restrictive than Windows Mobile.
With the first release of Windows Phone 7, it was not possible to create a third-party application that communicates with a desktop PC and accesses to contacts and events on the device.
Microsoft released a new version of Windows Phone 7.5 (Mango). But if the previous limitations no longer exist, unfortunately the access to contacts and events is "read only". It is not possible to create, modify or delete a contact or an event. Furthermore, it's only possible to see the individual occurrences of a recurring event, and not the original recurring event with its recurrence rule. So presently, it's not possible to synchronize contacts and events.
Microsoft finally released a new version of Windows Phone 8. But if it is now possible to create custom contacts, it is still not possible to write a calendar event on the mobile device. Let's see which functionalities will be provided in the next version of Windows Phone...