Google Voice - Incoming Calls

When I'm in Canada I turn off my cellular service to avoid crazy large charges and rely on Google Voice.  Of course that's only good when I'm connected to WiFi, but that's about 98% of the time. Placing calls is a no-brainer, but receiving calls requires enabling a feature in Account Settings in the Google Hangouts app, as shown below.

https://support.google.com/hangouts/answer/6079064