I would like to set up a phone service that provides automated information to users who dial a number on an ordinary telephone - think "Dial-A-Joke" or something similar ("press 1 for this, press 2 for that, ..." and then the system reads off whatever you chose). This is often called an Interactive Voice Response (IVR) service. The service should be installed on a generic server from a hosting provider with no special hardware - an Amazon EC2 instance, for example.
It seems that twilio would be perfect, because it handles all the telephony and your server drives it by responding to ordinary HTTP messages. Unfortunately, it isn't available yet in my country (Great Britain).
Can I set up what I want using Asterisk? I can find tutorials on setting up Asterisk on hosted servers (just by searching google for "asterisk ec2") but none of them explain how you go on to pick up an ordinary phone and dial the Asterisk instance you just set up, or how you configure it to respond with given messages.
Just to be clear, I'm aware that hooking up to the plain old telephone service will cost something. I would like the option to have my users pay a small per-minute fee to cover this, or to take up that cost myself (not sure which model I'll use yet).