Small Business Directory Service Ideas? Maybe a beer?

I need your input for this:

Say a Network Marketing company needs to provide a directory service for all its agents. This directory would be accessible by calling a toll free number. On calling this number, the end user would punch in the agents name such as MANN by pressing 6626.

Now this service is provided by PBXes, but if you could not afford a PBX, what off the shelf software could you use.

A beer keg for the best recommended workable solution!