I've had this problem since the GB update in July. For me, it doesn't actually drop the BT connection- my phone stays paired to my car. If I'm on a call when I get an sms/mms message though, it transfers the call to the handset as if I selected that option from the call screen. Very odd and frustrating.
I've had conversations with both VZW and HTC about this. The VZW rep told me that his system showed an alert for Samsung phones doing the same thing following the GB update, but nothing for The Droid Incredible 2 (maybe this is a GB thing, and not an HTC thing). His solution (which didn't work): factory reset.
The first HTC rep I spoke with said he had never heard of this, and could not find any notes on this issue in his system. He transferred me to someone else who told me that there are aware of this issue, and that they are only seeing it on phones that received the OTA versus those newer phones that shipped with GB. He said that I should try to exchange my phone for a new one, but that if I couldn't, I could send mine to HTC for a repair (yeah right), or wait because HTC is working on a fix via OTA to be released at an as-of-yet unknown time.
I got mine at Costco, so I guess I'll see what they say about an exchange...