One interesting feature in Twitter 411 service. This mashup lets users create own programmable Twitter bots. They are so calling messaging bots - so they will respond to direct messages.Service lets you register (reserve) some keywords (words, direct messages started with) and define your own reactions (including your own CGI scripts) for the reserved words in the incoming messages. Here you can see more about building your own information systems on the top of Twitter and how you can easily create your own Twitter bot.
But if you will simply send any DM to Twitter user t411 and the first word in your DM is not reserved for the service you will get answer from the default service - talk robot. Of course, it is not a famous Eliza from J.Veizenbaum, but anyway it can support the conversation, so you can talk. Try to send DM to t411 (you must follow to it first, of course) and talk with the robot.