[agildehaus]

It's difficult to enter the world of telecom IVR, the barrier of entry is very high, and to do anything at a large scale requires a large up-front investment.

Twilio makes telecom IVR as simple as writing a web application, and they're very affordable with no up-front costs.

I've written custom emergency notification systems, call-in contests, intelligent call forwarding systems (you could replicate Google Voice). Any phone app you can think of can be constructed.

[rebel19]

Twillio is great for getting a small app out the door. But if you need to scale it and get any advanced form of call control it doesn't support it. It also is a lot more difficult to move away from it if you need to scale out and use other systems. With Tropo you can integrate it with Adhearsion and then as you need to scale move it to Rayo or Asterisk......and you also are not limited to the currently supported countries with Either offering. Tropo allows you to set up your own endpoint in a country they don't support and will integrate that in. So if you are in a South American country, or any place that Twillio doesn't support it is the only game in town.