I think you underestimate the degree of vendor lock in Apple has. If you are a heavy user of iMessage, and you are a participant in multiple iMessage group threads, and you switch to Android, you will never be able to participate in those threads again. There's no way to convert an existing iMessafe thread to a hybrid MMS one without getting every participant to delete the old thread and start a new one. Good luck communicating that fact to all of your contacts

Every time I post this on HN I get a bunch of people telling me you can deregister your phone number, or start a new thread, but iMessage won't convert its own threads to MMS automatically. Every participant in every thread has to delete it. This is considered expected behavior by Apple.

If you want uninterrupted communication with your contacts, and you can't afford a few missed messages, you have no choice but to stay on iPhone​ forever. SMS is dead. Apple owns your messaging identity now, and it's platform locked.