I have an 08 Altima w/nav and I sorry to report that Microsoft, HTC, and Nissan have managed to continue to propagate this sorry excuse for a "feature"!
This phone is going back to Sprint!
As it turns out, this has been a known issue discussed since last Nov. in the XDA with no resolution except downgrade to WM5 which isnt a solution for the Diamond.
http://forum.xda-developers.com/show...=1#post2669889
The new Sprint Diamond Touch has this same unusable BT connect to my car
. My 6700 with BigJ worked perfectly as well as the wife's Kantana and Kantana II.
Considering how the switching the headset back seems to fix it with hassle, I am wondering if the problem might be the new BT profiles being added in the new WM6 software and is confusing the car BT when it auto-connects. Sounds like it maybe trying to use the A2DP profile instead of the HFP profile. Perhaps someone can play with disabling all but HFP.