I spent last week in Japan and once again came to appreciate the power of being able to use my mobile phone's WiFi calling feature. It allowed me to call home at will without having to pay extra fees usually associated with using my mobile phone outside of North America. Of course, your mileage may vary depending upon which carrier you use.
I have my mobile service through T-Mobile. When I landed in Japan, I got a nice message on my phone saying that I could text and use data without any additional fees. Should I wish to make calls, it would only be $0.25/minute. It is always nice to get a reminder from your carrier letting you know the limitations on what you can do while outside of your regular service area.
I got to my hotel and immediately connected my phone to the Marriott WiFi service. Then I put my phone in airplane mode being sure to keep the WiFi still on. Then I called my wife and everything worked. I know I didn't have any long-distance charges as the phone didn't have the ability to connect to Japan's mobile phone carriers. I could talk to my heart's content without racking up a phone bill.
My wife would head to bed during my lunch time in Japan. While I could have connected to my office's WiFi, I actually opted to spend 50 cents and called her for just a couple of minutes. It worked well and I didn't mind spending a little as I had been asked not to connect my personal phone to the corporate network. The Japanese pride themselves in following rules and so I try to as well when I am there.
Yes WiFi calling is a great way to call home when you are traveling internationally. If you are not sure if your phone will use WiFi or the mobile carrier, just put it in airplane mode and that will force it to use WiFi. Then you don't have to worry about incurring any additional costs on your trip.