Take a look at Tropo — in my opinion it's better than Twilio, not least because scripts can be written in Ruby and hosted on Tropo, and has (or had) much better international support.
And twilio works great with ruby, callinwith.us is a rails app.
Although if I needed international support I guess that would be an issue. Being a naive American has some perks though.
You've got my email now so we can get international calling enabled for your account if you'd like. Just reply in our other thread and let me know.
Twilio: "Twilio does not offer phone numbers from outside the US and Canada, and you can’t port international numbers to Twilio." http://www.twilio.com/faq/international
Tropo: "We offer local numbers in the US and 40 other countries - here's the full list of available countries, note that these are also free for developer accounts" https://www.tropo.com/docs/scripting/international_dialing_s...