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.
We've got great coverage for voice in countries all over the world: http://www.twilio.com/pricing/international-calling-rates You can both call to those countries and receive calls from them. We also just recently added local numbers in the UK in beta (http://www.twilio.com/uk-voice), which is just touching on the surface of what will be coming outside the US.
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.
Sorry but a year after I chose Tropo over Twilio, Tropo still wins:
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
That's my issue with Twilio too, I need UK inbound not just outbound - calling US numbers from the UK is (apart from with VoIP phones) pretty expensive.
You missed that point: with Tropo you don't need "an app", you can do it all as a Ruby/js/java/etc script hosted by Tropo. It's obviously limited in scope but very useful for small apps
And keep in mind that the interface for Tropo and Adhearsion are very similar so if you need to expand beyond using Twillio or Tropo it gives you a lot of options with less pain...you can also use Adhearsion with Tropo as you are transitioning an app.
