Finally figured out enough stuff so I could poke around some more.
The only setting I had to change after installing one of the VoIP cabs I had was one flag in one registry setting.
According to MSDN the default setting for "Features" under HKEY_CURRENT_USER\ControlPanel\Phone for a CDMA phone is 2B820, and that GSM cab you had was setting 206C7D8.
After combining the flags, and take away flags one by one, it seems the only flag that really matters is SHDFL_PHONE_LOCKFACILITY. (Doesn't really make sense to me, but it worked. I was expecting one of the other flags.)
That makes the setting 2B828 (instead 2B820)
MSDN: Configuring CDMA and GSM Radios Default Phone Features