THE SOLUTION TO YOUR PROBLEM:
If you are a fan of WM dialer but don't like the fact that you cannot change the volume during a call, this CAB by HallengreeN replaces the HTC volume control for the WM default volume control, which will allow changing volume during call.
http://www.4shared.com/file/73168996...llengreeN.html
try this...this solved my problems it not only replaces the HTC volume control but it installs a different one that works and is more functional.