I'm trying to create a voip based IVR service that interacts with a web application. From what I understand, adhearson runs on top of asterisk. What else do I need to have on the server to satisfy the equation? I think I need a way for asterisk to connect to a voip account. I'd appreciate any help and/or phrases to google.
If you want to build your IVR quickly and easily you'd be better off looking at something like tropo.com (tropo's parent, voxeo, own adhearsion) or twilio.com, they've done a lot of the grunt work for you and setting up Asterisk is not for the faint hearted.
If you want something half way in between you could open a cloudvox.com account and run an adhearsion process on your own machine. In that configuration the call will be processed on the cloudvox Asterisk servers and make calls to your adhearsion daemon to control the call.
As sipwiz noted, we can do this stuff at Tropo (thanks Aaron, for the mention).
Beyond the question of how har it is to set up Asterisk, ask yourself if you really want to maintain it. You can set up a web server under your desk, but for most production web apps, you're probably paying a hosting company to run it for you. That's what Tropo does. We take care of the telephony bits and let you focus on building your application.
If you do want to go the Asterisk route, we do sponsor the Adhearsion project. There's a decent tutorial for installing Asterisk and Adhearsion at http://mah.everybody.org/docs/asterisk/adhearsion-setup.html
Or you can grab an account on our Adhearsion sandbox and give the framework a try without having to first install Asterisk. http://adhearsion.com/getting_started