MacDialer is a small application that operates as a menu bar or Dock application. It provides a menu-based system to dial the records in your Address Book as well as an Applescript interface that enables features such as command-line dialing and an Address Book plugin. MacDialer lets you dial using your Mac's internal modem or speakers, bluetooth-enabled cell phones, and certain VOIP systems.
MacDialer has been discontinued. Other than possibly updating for future OS X versions, no active development will be taken on MacDialer. That means that MacDialer is now completely free to download and use.
There are a lot of good telephony apps for Mac OS X that are in active development by some very talented programmers. I recommend the following applications for anyone interested in actively supported and growing phone dialers.