If there was a moment for me where the light went on for Telco mashups, it's when I saw the Ruby on Rails Screncasts. They are a bit goofy, but if you actually sit through one, and realize what you are seeing - it's earth shattering. It's earth shattering especially when you realize that the other parts of telephony applications, such as scripting front ends, and web services back ends, have very similar productivity gains associated with them. Just check these out... especially the Flickr screen cast. Be careful that you don't drool.