I have a Nokia 3650 phone, which I use with two different computers at work via Bluetooth. My main desktop system, an Apple G5, keeps my address book and calendar. My Dell PC is used for Bluetooth Serial Port access, so I can sync AvantGo without having to pay 2 cents/KB to do so.
Every time I move from the Mac to the PC or from the PC to the Mac, I have to re-pair the phone with the computer, or nothing works.
Now I just need to wait for Apple to add Bluetooth Serial Port support to OS X. Doh.