[akalsey]

If you're looking for more options, there's a LOT out there. Think of all the automated voice systems you interact with on a regular basis.

In the open source world, you could install Asterisk yourself and use something like Adhearsion to develop your apps. Adhearsion is an open source framework for building Asterisk applications in Ruby. http://adhearsion.com/

Whistle from the 2600hz project could be of interest, too. http://www.2600hz.org/whistle/

To build telephony applications in Java, you can use SIP servlets, a Java standard (look up JSR 289 and JSR 309). Because the Java standard is extremely low-level, we open sourced the framework we use for building Java speech applications. See Moho at http://labs.voxeo.com/moho/ or https://github.com/voxeo/moho

You can also take a look at at VoiceXML, a W3C standard for building telephony apps. VoiceXML is how the big boys build telephony applications. There are a number of commercial and open source VoiceXML products, and tons of hosting companies. A search for "VoiceXML Hosting" will turn up several thousand options. Many of which will work internationally.

And of course Tropo, as already mentioned, has an open source core as well as a ton of other fun open source stuff. See http://tropo.com/ and https://github.com/tropo/

[runT1ME]

I'm a fan of Tropo and have recommended it to clients, and overall think Voxeo is the team to beat in the telephony market. However, I feel you're exaggerating a bit here:

>VoiceXML is how the big boys build telephony applications. There are a number of commercial and open source VoiceXML products, and tons of hosting companies. A search for "VoiceXML Hosting" will turn up several thousand options. Many of which will work internationally.

VoiceXML is great for IVR type applications (along with CCXML) but it is not suited to a lot of the types of applications developers use for Twilio/Tropo.

>And of course Tropo, as already mentioned, has an open source core as well as a ton of other fun open source stuff

This statement is true if you guys open source PRISM, your SIP server, but until that happens (has it happened?), it's a little disingenuous to say that Tropo's "core" is open source when it relies on a proprietary SIP server to do all the heavy lifting.

[akalsey]

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.