There's not a lot of news on that front (not yet). For RR there used to be an application for PhoneControl which required the Widcomm Bluetooth stack. There is currently a plugin which uses Bluesoleil (same limitations you probably know). For phones which support GSM commands (i.e. SonyEricsson) and have some sort of serial port connection (cable or Bluetooth) you can use "freefone" which is old and has no way to route audio thru the PC.
The best solution would have to be hardware based to deal with audio, connection and basically mimic what you see in many car stereos today (and even that may still be limited to whatever compatibilities issues there may be between phones and such). I'm saying this specifically because I have tried a few different hardware bluetooth devices and there are still limitations with the way certain phones communicate and which features they support. Chances are you'd have no problem with mainstream phones (i.e. iPhones and SonyEricsson generally have good connectivity), while Android and Blackberry phones can be plain awful with connectivity (as far as providing interface for polling contacts, call control, etc). Still having a solution that works perfect with a good number of phones is better than having little to no support in most phones.