Adhearsion is not a rails plugin. Rails is certainly hot though. After all, the web is hot. Telecom, at least historically, is not at all hot.
Asterisk, the defacto standard, has a fairly tough-to-get-into codebase. Maybe adhearsion can do something.
Your phone is actually a universal remote. There are mad possibilities for controlling doors, video games, and all manner of electronics.
There are lots of fun hijinx you can get into: spoofing caller id, locking out automated telemarketers, integrating with instant messaging, ETC.
Adhearsion is open source software that abstracts away this technology with ruby in an extensible, easy to understand way. “Weasels have destroyed the phone system.” Word!