For those that may want to use the WiFi calling feature, which Verizon conveniently omitted in the first itineration and T-Moblie users enjoy right now, you can do this using the LINE APP and LINE Premium call. It's not free but it will not use up your data, roaming or voice plans and very much cheaper. To assure WiFi use you would need to go into "Airplane Mode" FIRST then enable WiFi on the iPhone 6/6+. Hope this helps you international travelers wanting to make calls overseas. May countries, especially Japan where I frequent, have free access WiFi in all the major cities. So I save a TON on roaming charges instead of renting/and or purchasing an international sim. ~ Cheers!
I just tested SKYPE using "Airplane Mode" + WiFi and it works fine in Japan. Saying that I will assume it will work in Europe as well [provided there is WiFi available]. Hope this helps.