My deal is that I have the "talk forever" plan with TMobile that allows unlimited use of the phone over any WiFi. With that plan, a TMO rep said that I will NOT be charged for phone or data use, but I needed to be careful because if I started on WiFi and it transferred to roaming I would then be charged. Therefore, when making calls on WiFi, I did as Krabme suggested and turned off my "mobile network" under Manage Connections to prevent issues. TMO did say that they don't "guarantee quality of calls" when using that system but I found phone calls from Italy to USA to be seamless. Also, be aware that calls TO a foreign number will be charged as if you were calling a foreign country from your home country. YOu need to make and receive calls to and from US based numbers to keep it free...