There are two potential issues at play:
1) If the phone rings and/or blinks, but the phone does not pick up even when you press the "Send" key, or answers only several seconds after you press the Send key, here is the solution:
http://forum.ppcgeeks.com/showthread.php?t=40427
2) If the phone flashes but does not ring for several seconds AFTER the phone starts flashing because of an incoming call, here is an option (by going with the default WM dailpad skin):
HKLM/Security/Phone/Skin/Enabled=0
Setting this value to 1 will re-enable the HTC skin.
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