Amazon.com Product Description
AT&T offers a phone that functions as both a regular cordless phone and a PC phone. The cordless handset has a 900 MHz transmission and 30-channel autoscan for secure calls and clear conversations. Use the phone as a PC phone and enjoy the low-cost benefits of long-distance Internet calls. The sound quality is a big improvement over the traditional PC microphone and speaker setup. The phone is also headset compatible (2.5 millimeter jack) for hands-free use. In order to make internet calls, you will need a PC running Windows 95, 98, or equivalent; a sound card; and an internet connection that supports VoIP and VoIP client software.

From J&R Music and Computer World
The ATT 6100 is a great cordless telephone for your home. It'll connect to your phone service jack and can be used as a regular telephone with optimal clarity and cordless range throughout your home. BUT THAT'S NOT ALL! You can connect the ATT 6100 to your PC computer so you can take advantage of Internet phone call services. You can actually call long distance at remarkably reduced rates - even FREE.