As noted, you'll also need to have an existing US-based mobile or landline phone number, so in that sense, Google Voice is not a free phone service but rather an add-on to your extant services.

Except, it’s much higher than you expected thanks to roaming charges for using your phone ... Google Fi (at $10/GB to keep high-speed data after the 50GB fair use policy) or $200 with T-Mobile ...