Hey, you also saved my ass...man I tried everything...all kind of modems were not working, USB 3G Modems, Telephones connected through USB or bluetooth..anything...
Just a comment, a needed a restart after the Registry modification.
Thanks a lot!!
It took me months but I finally got the same problem fixed.
Here's what I did:
Completely remove all traces of your modem software and drivers.
In Regedit, I went to:
There should be a string called "Installer32", if not, create a new string and call it "Installer32" and set its value equal to "mdminst.dll,ClassInstall32"
Re-Install modem software and Drivers.
Worked for me.
Hope it works for you as well.