automated phone call program

There is a Telephony API for windows called TAPI... but obviously this is no good for linux, so you'll have to search for it's competitors. "Telephony application" will probably be a decent search term to begin with.

Alternatively, check out the specs for your dial-up/voice modem, and see if it lists any APIs that it is compatible with.

Depending on what you are doing, Asterisk is either 'really cool' or 'total overkill.'

Another option is the kernel API.

You're going to need some point of interface between your software and the public phone network. There are two main ways to accomplish this: one is to get a hardware interface (technically called an FXO) that plugs into a standard analog phone line, and communicates with your software via a kernel driver. The other is to subscribe to a voice-over-IP provider and communicate with their server over the Internet, probably using the SIP protocol. As far as I know, either one of these approaches can be used with Asterisk.

If you have a modem plugged in I believe it should be as simple as sending "ATDT " to the appropriate COM port. You can hang up with +++ (standard escape sequence) followed by ATH.

A more complete list of commands is at http://www.zoltrix.com/support_html/modem/USEMODEM.HTM