The problem with those two standards, is that they are not being followed well, and are also far to granular for most implementations. Twilio was a real breakthrough in terms of getting projects off the ground fast.
Tropo and Plivo have also emerged as additional options in that space.
The main problem I see with this new API is that there really is no incentive for me to go to them over Twilio, Tropo or Plivo. What Twilio doesn't provide is covered well by Tropo and Plivo. The only interesting thing offered is unlimited inbound per channel, however, if you have SIP, you can get it cheaper from companies like FlowRoute (http://flowroute.com/services/inbound/) and pay $18 per channel, rather than $27.
Compare this with: Twilio - first mover, known reputation, strong funding. Tropo - backed by Voxeo (over a decade in business), offers many enterprise-grade things; Prism (IVR server) is opensource. Plivo - a lot cheaper than everyone else, and offers open source layer for FreeSWITCH.