Phone numbers disappear in Address Book

I just realized that many of my contacts are deleted from my phone after synchronizing with my mac. In Address Book (Apple) the contacts are still there, but some numbers are gone. I have searched back in Time Machine and found that the numbers are missing all the way back. This is very strange, because I know I have used the numbers lately (some of the missing numbers belong to close family and other people I know I have spoken to). How could the numbers disappear from both the Address Book AND from the history of Time Machine? I got Snow Leopard a few weeks ago, maybe that has something to do with it? My phone is a Nokia 6300. I have Entourage installed, but I only use it very rarely. Someone suggested Entourage might cause the trouble? The contacts miss the same data in Entourage address book as in Apple´s Address Book. Any easy fix?