I have a Samsung S5. When I got to the United States, I turned off mobile data and I specifically selected the "deny access to global roaming" button. I have not used mobile data at all. After the first day, I got a text message saying I got 25$ of roaming charges. I thought maybe this was when I got off the airport and opened the phone, for a few minutes, I might have been downloading something. But today I got 3 more text messages saying I am now at 100$ of roaming charges.