I am currently looking around to see if I can get Mozilla Thunderbird and Sunbird to sync with my Sony Ericsson s710a phone. Currently I can sync with Outlook, but I like Thunderbird a bit better. So far I have found two approachs:
1) MobileMaster: Lets you sync both you calendar and address book. The only problem is that it costs $29. That is not so bad I suppose, but still… http://www.mobile-master.com/index.html
2) Sync4j: An application framework that lets you sync a lot of different programs and devices together. It looks like it is just getting started, but I think it could be pretty interesting in the future: http://www.sync4j.org/
I think I am just going to use Outlook for a while longer until this is sorted out.