[steveholtam]

I think this mentions the same thing, just worded a bit different. But I have no clue, just trying to help...

"Here are the registry settings for UNKNOWN callers.

Set your normal ringtone from the Sounds panel, browse to HKCU\ControlPanel\Sounds\KnownCallerRing0 and make sure your Sound string points to the file you want. Now go to HKCU\ControlPanel\Sounds\Ringtone0 and change Sound to point to a different file. Wait 10 seconds, soft reset et voila.

To test it, I removed my home number and called my device, rings with the unknown caller. Re-add your number and it will ring with the known tone."