Turn on iCloud? prompt keeps popping up

My iCloud is activated, with nearly all features enabled except for iMessage. I'm not sure if it's related, but there's this annoying pop-up that says "Turn on iCloud? Your network provider may charge for SMS messages used to activate iCloud" that keeps appearing. I keep dismissing it, just to be safe, in case my phone has been compromised or something. This is the first time I've encountered such a pop-up since using iPhones. Anyone had this popup before?