International is hard. I know from experience. That's where Tropo has one clear advantage over Twilio. Tropo is built on the Voxeo network, which has ten years of international experience, is deployed world-wide (seven data centers), and integrates directly with most of the carriers around the world.

I believe Twilio integrates directly with a single carrier (Level3). Last I checked they use/resell bandwidth.com for most of their calls.

-Jonathan (Voxeo CEO)