"Your carrier may charge for SMS messages used to activate iCloud."

I logged out of my apple account once and when i logged back in, this kept popping up. At first it was worse but now it only shows up when i go to iCloud in settings but it still irritates me and i don't understand the reason. There are no SMS messages for my carrier to charge me. iCloud works just fine. What can i do to make this disappear and never show up again?