Yes. If you already have a Google Voice number, the app works in most countries over Wi-Fi or mobile data, and calls to US and Canadian numbers are almost always free when they go through the app.
The catch is how the call is placed. Google's calling rates page says that if you call from abroad over your carrier's network, you pay international rates plus whatever roaming your carrier adds. Use Wi-Fi or data and route the call through Voice instead. The app shows a message confirming whether a call is free or paid, and if you see no message at all, the call isn't going through Google Voice.
What it costs and what doesn't work
- US and Canada: almost all calls are free, with a few destinations at 1 cent per minute.
- Other countries: billed per minute from prepaid credit at the rates in your Voice settings.
- Texts: you can only send texts to US and Canadian numbers, though you can receive them from anywhere.
- Blocked locations: Google lists calling as unavailable in Crimea, Cuba, Iran, North Korea, Sudan and Syria, and Chinese carriers may block some calls.
- No emergency calls. Use your phone's regular dialer for local emergency numbers.
Set it up before you leave
Personal Google Voice plans are only available in the US, so create your account and pick or port your number while you're still home. Workspace business plans work in more countries.
Also keep the number active on long trips. Google reclaims numbers with no activity after sending a warning. Making a call, sending a text or listening to a voicemail before the reclaim date keeps it, and you get 45 days afterward to recover it.