Somewhat surprising/disappointing to me was that now you can't even send SMS to a number that initiates the conversation--this would seem to be a pretty clear opt-in indicator. Because of that, I couldn't find a way (through Twilio) to get around the registration requirements just to send SMS to my own number for development purposes to try some things out. The registration workflow and UX is also comically terrible and confusing.
It's a shame as I think there are some legit non-spam use cases for SMS as a messaging platform, but considering you now seemingly need to pay, fill out a bunch of annoying/buggy forms, and wait for days to who-knows-how-long before sending a single message in development, I'd say it's been pretty well destroyed as anything a dev would ever play around with. Who's going to do all that before writing a line of code?