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.
Southern Living on MSN4d
The Landline Is Back, Kind Of
In the age of cell phones and 24/7 access to everyone and everything, one editor misses the simpler days, where just one waxy coiled cord kept you tethered to the wall—and the world.