Twilio will succeed simply because they've reduced it to being ridiculously easy. I mean, a complete non-coder could practically put together a working app base

Twilio will succeed simply because they've reduced it to being ridiculously easy. I mean, a complete non-coder could practically put together a working app based on Twilio, which I doubt is the case with any VoiceXML provider. I personally wrote a phone-in support service, company extensions directory and voicemail-to-email service with Twilio in literally a couple hours. It now integrates seamlessly into a new support system I'm launching for one of my companies in the next month or so. Twilio's part was so easy it was an afterthought, but will really make my new service shine. Couple that ease of use with their super affordable and transparent ($5/mo + $0.05/min for an 866#) pricing model, and you've got a winner. I can appreciate the need for standards, but sometimes they're simply trumped by easier and better technologies. Look at the progression from SOAP -> XML-RPC -> REST for example :)