My friends and I have never ran into this issue switching from iOS to Android. The main thing to do is to disable iMessage on your old iPhone before you get rid

My friends and I have never ran into this issue switching from iOS to Android. The main thing to do is to disable iMessage on your old iPhone before you get rid of it; that should unregister it on Apple's servers. If you do that, then you should be unregistered unless you have another device hooked up (i.e. Mac).