I have a BlueAnt ST# speakerphone, but I am sure it isn't the problem here. I just bought the Thunderbolt and when I paired it to the Blueant, all went well until I tried to make my first call. The voice prompt volume is just too low, so I started doing some troubleshooting. I found that when I activated the voice command from the BlueAnt and then hit the volume button on the phone, a popup came up on the phone showing I was adjusting the "Bluetoot In Call Volume". I also noticed that it was set at halfway by default. Adjusting it upward helped with the voice prompt volume from speaker, but it only lasted for that call.
I then went into the phone to see if I could make a permanent adjustment to that volume setting and it is nowehere in the settings. So, everytime I want to use my blueant to make a call, I now have to reach down to my phone and nudge the volume up after the voice prompt starts, which is completely unacceptable to me. HTC should allow us to make a volume setting to adjust that permanently. They are probably trying to save their legal rears by forcing this issue, but it makes the phone almost unusable in my truck, so it may get returned soon.
BTW, I also tried Audio Manager and a number of other apps, but none of them made a difference.
Has anyone found a workaround for this issue yet that doesn't involve rooting the phone?