been doing it for years now (since grandcentral) - are you trying to call out using your gv number, or using the gv app? - or are you testing calling into your gv number? - if you call out using the app, the current app uses a random number so it no longer works w/faves - try dialing your gv number & using option 2 to place the call.
I use a calling card app to do the dialing for me.
you can also use the web app to place the call out.
if you're testing calling IN to your gv number, then make sure you have gv set to show you your gv number on inbound calls instead of the caller's number (I know it's a little inconvenient to lose caller id, but you want FREE CALLS... right?)