Comment by pmarreck

People think iMessage has entrenched iOS but what's actually happened is that iMessage has entrenched the POTS phone number system, which is (frankly) unregulated shit.

You can actually iMessage people with just an email address, but in practice I don't think anyone actually does that since you can't also call them by that identifier (but now you can use any number of services to call digitally while skipping POTS phone numbers entirely)