This is not a dedicated intercom, but one that actually connects to your existing home phone.http://www.smarthome.com/5070CA/Door-Phone-Intercom-System-DP28SF/p.aspx
Apparently, if you combine this with an existing, electric door strike, I can use it w/ my existing phones. When the door button is pressed, your phone rings and you can talk to someone at the door. Then you hit '*' on the phone to buzz them in, this is in addition to the standard indoor button.
I'm probably going to try it but curious if anyone has already. IIRC, wheelz suggested one but it was more of a true, dedicated video intercom. This is more low budget, but a little more clever.