I believe Ericsson can be used internationally for everything Twilio does in the states. They're a bit more corporate than Twilio, and their website is hard to navigate, but once you get in contact with them they're more helpful.
They are not able to provide long codes (10 digit phone numbers) for messaging in the States, but they can use long codes for messaging internationally.
In the states you're limited to Short Codes, but they do offer MMS support, which one-ups Twilio. I believe they also have a higher send rate, but I don't remember the specifics. Ericsson also has mobile payment support (charged to the carrier), where Twilio does not.
My research was specifically for messaging, but there is voice functionality as well.
Overall, Twilio is a lot more developer friendly. I think I waited something like two weeks for a callback from Ericsson, which would never happen with Twilio. But if you really need international phone numbers and advanced features, take a look into Ericsson.
I use Twilio now, but I don't use Ericsson yet. Chances are my product will end up using a combination of both, but the nature of every product is different so do what's best for you. Twilio can text/call internationally, but not with local numbers, which I believe makes the cost quite high on yourself and your users. Apparently there are also other solutions I haven't looked into yet (see other comments).
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/
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.
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.
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.
They are not able to provide long codes (10 digit phone numbers) for messaging in the States, but they can use long codes for messaging internationally.
In the states you're limited to Short Codes, but they do offer MMS support, which one-ups Twilio. I believe they also have a higher send rate, but I don't remember the specifics. Ericsson also has mobile payment support (charged to the carrier), where Twilio does not.
My research was specifically for messaging, but there is voice functionality as well.
Overall, Twilio is a lot more developer friendly. I think I waited something like two weeks for a callback from Ericsson, which would never happen with Twilio. But if you really need international phone numbers and advanced features, take a look into Ericsson.
I use Twilio now, but I don't use Ericsson yet. Chances are my product will end up using a combination of both, but the nature of every product is different so do what's best for you. Twilio can text/call internationally, but not with local numbers, which I believe makes the cost quite high on yourself and your users. Apparently there are also other solutions I haven't looked into yet (see other comments).
http://www.ericsson.com