VoiceXML and CCXML are suited for most telephony apps. We've seen conference calling, dating, virtual Number services, notifications, and lots more on XML telephony platforms. Twilio and Tropo Apis are each subsets of what Vxml & CCXML are.
Vxml and CCXML are more complex, sure. And for that reason they may not be suited for the same developers targeted by cloud Apis.
Prism, the app server platform Tropo.com runs on, is not open source. But because Tropo core is written to the JSR call control and media server standards, Tropo will run in any server that implements those. Mobicents and Sailfin are two open source options.
Vxml and CCXML are more complex, sure. And for that reason they may not be suited for the same developers targeted by cloud Apis.
Prism, the app server platform Tropo.com runs on, is not open source. But because Tropo core is written to the JSR call control and media server standards, Tropo will run in any server that implements those. Mobicents and Sailfin are two open source options.