Some people may wonder, “Hey, how can I use iSync with Entourage?”
The short answer is that you can’t, but if you want to regularly push your Entourage data to Addressbook, you can do that too.
The best place to start is with /Library/Scripts/Mail Scripts/Import\ Addresses.scpt, a script that will import your addresses from a variety of email programs and dump them into Addressbook.app.
It doesn’t sync – so you’ll have to remove your old information in Addressbook prior to using this, and you could cut and edit the Apple script into one that does exactly what you want.
I will be working on a way to automate the removal of Addressbook’s entries, importing of Entourage, and then you can use iSync to push to your mobile phone. I don’t know when I’ll have the time to devote to this, however, so if you help yourself, I’d love to hear about it.