"CAPTUAL" WHERE WE STAND:A-F Yup, tried all these and even went out and bought a NEW Motorola BT H15 and it still sucks...AppleCare says it's a bad BT...Next issue to be addressed by SJobs!!! 
Mine connect to my Eclipse Bluetooth and Plantronics simultaneously and calls go to the Eclipse maybe because a stronger battery/signal it seems which is good as I don't have to remember to turn off the Plantronics, it then connects to it out of the car 'most of the time'.
However, it connects and disconnects like crazy indoors at times when the Plantronics and the iphone are inches apart.
I still can't answer the phone when its connected to the Plantronics without the call going to the phone, and me having to go to settings, bluetooth, etc.
There is supposed to be a fix/update coming by the end of July for this and the proximity flaw.
I like this phone for the most part and have 20 more days for them to fix the bluetooth, or I will look at something else.
I've been experiencing an issue with not getting a call notification or a ring from the blue tooth built in my Nissan Titan after upgrading my 3GS to the iPhone 4 version OS. I even updated to the 4.0.1 and had no success in getting a ring from my audio system, so now I will not be able to catch incoming calls while driving.I've submitted my comment to Mac on the issue.
Jason
If you have not yet, please contact Apple about this problem. When I called to advise someone they had no idea of a issue with Bluetooth connectivity