I’m currently in Nepal as a volounteer, where I have bought a Sim-card, and put it into my iPhone. Everything works like a charm, the 3G is super fast, but I still keep getting the famous iMessage activation error, or just waiting to activate. I’ve tried restarting the phone, logging in and Out Of the apple-ID, turning messages on and off, reinserting the sim-card, etc., but still there is nothing happening! My old Danish number is still greeted out in the settings, while I have put my new Nepali number into phone-settings. I really hope this isn’t a bug with iOS 11. I haven’t really found a solution that works so far, maybe because I’m in Nepal?