Full disclosure: Both AT & T and Verizon websites state that there will be charges for wifi calls made to international destinations, With airplane mode enabled I have never incurred any charge for any calls to any country. They have no clue where you are. They do NOT mention enabling airplane mode for a definite reason (charges). Just relaying how it is for me with my S7 and Verizon.

When you are out of country make a one minute call to a location NOT in the USA ...airplane mode on...wifi calling (NOT wifi assist) enabled. Check your account in a couple of days and see if there are any charges. Worse case you might have a one minute charge but I would be shocked if it was there.

I had no clue that this worked until I unexpectedly received a call on my cell while in SXM from my bro in law in Virginia. How could that happen? I'm in airplane mode....but I am in my room with a wifi connection enabled., Been using it ever since that epiphany (after a couple of test runs)