Ok. I checked out a Curve today and loved it - almost - great size, great look, good feel, keyboard good. I really want to get it except for one thing...built in GPS. I use my built in GPS on my 8800 all the time. I realize that not everyone is a big GPS user and different needs for different people. I know that there is mapping software on the 8300 but not GPS. If it weren't for that one teensy weensy little issue, I would have the 8300. I finally concluded that if I were going to go back to a BB without GPS, I would go back to a Pearl. So, now that I am used to my squeeky 8800 and have mastered the smaller keys on the 8800, I guess I will stick with it...for now...I sure do like the Curve though...hmmm.
You can use the bluetooth GPS puck and a bluetooth simultaneously. Just be sure to turn on GPS puck first and be sure it is receiving a signal. Once bluetooth GPS is activated you can use bluetooth headset with no problem. My Jawbone and Motorola bluetooth headsets work work perfectly with my TeleNav GPS puck.
However, I'm not sure about bluetooth built into an automobile sound system. I've tried my daughter's Nissan Versa factory bluetooth system and I can only dial using voice activation. Once the call is connected I have to use the Blackberry to carry on a conversation.