I don't remember the process exactly since it's been a few years, but I found a website that seems to explain it: Use a Google Voice Number from Outside the U.S.

I saved the step of making a US number by using my mother's phone # and had her tell me the confirmation code. But if you use someone else's number, you need to make sure that you turn off call forwarding once it's set up so it doesn't ring them every time you get a call. The cool thing is that Google voice gives you a dedicated number for free texting too, so I can keep in touch with friends that way.

(Apologies to everyone else for advertising. It's just a really good service.)