Check out
http://forum.xda-developers.com/show....php?p=3714509.
With these regedits, I get the behavior described in the post (initial ring followed by a fairly quiet voice announcement).
It's still a bit broken (why can't it announce the incoming call loudly enough for me to hear? Why can't there be a checkbox to cancel the ring if the call is being announced via a bluetooth headset?) but it does sort of work.
Edit:
http://ppcgeeks.com/forum.ppcgeeks/s...d.php?p=545329 discusses some of these issues, along with a potential fix for the volume issue that I'll be trying.