Google Voice has long been helpful for receiving phone calls regardless of the device you're using. That's assuming you want a conventional call, though -- it can be a pain if you're traveling and face roaming charges, or in those moments when you want to start a call away from your phone. Relief is at hand, however, as Google has started enlisting users to beta test for a data-only calling option. Sign up and you can soon use cellular data or WiFi for calls from Voice on Android or the web (iOS is coming), whether or not you're using a phone.
There are caveats. The beta feature can't use incoming call recording or transfer options when you switch on data. Key Bluetooth audio functions are missing (including button control to answer or hang up), and Obihai voice-over-IP devices won't work. This is a test in the truest sense, with known major bugs and an expectation that you'll provide feedback. All the same, the beta could be worth a try if Voice's use of the conventional phone network frequently creates hassles.