I've been using VC for a few years now, and I know the issue of 16khz sampling vs 8khz sampling over Bluetooth has come up before. Basically VC on the device was optimized for 16khz sample rate using the devices mic, then bluetooth headsets came into the picture and they only sampled at 8khz.
See this MS Blog entry for details:
http://blogs.msdn.com/windowsmobile/...-over-bth.aspx
The author of the Blog says:
"the issue with the solutions that make existing VC work on BTh headsets is that the recognition rate goes down. We would rather do the work to do a full 8 kHz model that meets our quality bar."
I often get bad recognition, but I can't say whether is was with a bluetooth headset or not.
Anyone notice a trend on their side?
Anyone know how/if Microsoft resolved this? or did MS hack 1.6 to get it to work out of the box?