Benjamin Stein draws attention to a nasty bug that occurs when you switch away from iOS/iMessage (via David Chartier):
Let me recap: I no longer have iPhone. My phone number isn’t associated with Apple, iCloud, iMessage, or FaceTime any more. But every single iOS device I have ever messaged in the past 5 years has my phone number cached! Every single phone will only try to message me via iMessage, not SMS. And to make matters worse, it fails SILENTLY!