Well, many BT phones do not work with iSync. This gives you a few options:
1) Return the phone and get one that does work with iSync
2) Wait (and hope) that it is eventually supported by iSync. I personally looked at the i605 a while back. It is a very new model and compatibility with iSync may come in the future ... a phone usually has to be out for a while before iSync will be updated to support it.
3) Sync manually in the mean time. this can be done by pairing the devices, opening AddressBook and clicking the BlueTooth button "on" and choosing Card-->Send this Card from within AddressBook. You can usually send the cards one at a time over to your phone and most phones will know how to accept them and add them to its internal phone book. It can be a real hassle time-wise if you have to do a whole lot of cards, but its really only painful that first time... afterwards its just a matter of adding the new cards. If some of your AddressBook entries don't really make sense to have in your phone (for example, an email address that you'll never email from your phone, you can skip those to save time. Generally, it IS really nice to have iSync support. I went from a Sony-Ericsson in 2003 that was supported, to a non-bluetooth phone in 2004, to my current phone that has BT but is not supported in iSync .... and man do I really miss having the iSync support. But ...if the phone is otherwise exactly what you want its worth the hassle of doing that manual sync at the outset and then it will be much easier from there.