Disable Carrier Phone Number for Google Voice Number This seems similar to this question, but that one doesn't have a clear answer, and this is a bit different.

Is there a way in Android to block all incoming calls that target the carrier number, but still receive calls that target the Google Voice number?

General problem I'm trying to solve: 
I use Google Voice and all valid callers have that number. The carrier-issued number was previously used by at least two people who are being sought by many debt collectors, and has started to get a large number of calls from scammers. I have no reason to ever receive a call at this number.

I currently use on{x} to manage various functions on my phone, but as far as I can tell, it does not offer a way to detect which of my phone numbers was called, only the number of the caller. I'm not sure if another management app (e.g. tasker or locale) would be more helpful, since I don't own either. 

I've been blocking numbers as they come up using AVG Anti-Virus, but since what I really want is a white-list for callers (those who know my Google Voice number) rather than a black-list it isn't really doing the trick for me.
Since Google Voice just comes in as a normal carrier call, there is no simple way to separate those calls. It doesn't pass any identifying information that the phone could use to identify it is a Google Voice call versus a carrier call. 

You can, however, change your Google Voice settings (on the website, not the app) so that it always shows your Google Voice number as the caller ID on incoming calls. This means you could just whitelist your Google Voice number and block everything else. Then you will receive only GV calls, but you will lose the ability to see who is calling since all calls coming to GV will just display as your GV number. You could then use the call screening features of GV to identify unknown callers. 

It really isn't an elegant solution and the loss of caller ID is a big inconvenience, but if you absolutely have to do this, it is about your only option.