Do you mean use the Hangouts app to make/receive calls and texts (via Google Voice essentially)?
I've done that basically with just a WiFi connection and it works fairly well, depending on the WiFi connection for the most part--the connection needs to be a fairly good one (as in fairly fast and with a good signal).
Yes, I've used it to call home to the U.S. from Italy & Japan, works well as long as you have a good internet connection. In Italy the hotel wifi was often poor and so it didn't work great, but it did work. Last week I was in Tokyo & the hotel wifi was very good & I didn't have any issues using it to make Google Voice/hangouts calls.
Anyone use their U.S. Google hangouts # overseas to make and receive calls and texts from U.S,?
There is old info out there about needing a U.S. ISP with a work around because the foreign country will recognize the ISP your on meaning your not in U.S. This is older info like I said.
2015 do you still need a ISP 'hack' in a foreign country or can you just call via Hangouts dialer with no problem?
The first time I used it was last spring in Italy, and it worked fine. I simply connected to the hotel's wifi & made my call using Hangouts. Did the same just last week in Japan.