Like Thunderbird and Windows Mobile? Try BirdieSync

Too bad Microsoft. You assumed making Windows Mobile sync only with Outlook (which happens to be your email-client software by the way) will keep people away from the competition. After all, Outlook is usually part of Microsoft Office, and you'd like to give the market as much incentive as possible to stay with you, right?
Well, the great thing about open markets is that people always rise up to fill a need. Someone's already written about syncing with Gmail (still using Outlook admittedly, but only as an afterthought), and thanks to BirdieSync, Windows Mobile users can sync your nemisis' (Mozilla) programs, specifically Thunderbird, Lightning, and Sunbird.
Even if I'm wrong about you Microsoft, consider this: after the 21-day trial, users will have to pay $19.95 to continue using BirdieSync–money that could've ended up in your pocket!
At least Outlook definitely sounds a lot better than BirdieSync. And don't forget how seamlessly Outlook works with the other Microsoft Office apps.