Cheaper (~0.65c) per SMS than twilio (~0.75c) in the US, great if you're already on AWS and support for sending to 200+ countries[1] but no MMS support that I can see...
No need for volume. SMS is dirt cheap on its own. For my clients we implement custom SMS solutions and our wholesale rates are free inbound and 0.0018 outbound. And we can activate any off-net number, don't need to own it even.