Welcome to the Internet age! The Yahoo! Voice services differ from your traditional landline and mobile telephone service in a few important ways. The Yahoo! Voice services are based on VoIP technology, unlike traditional landline telephone networks. VoIP is just a fancy acronym meaning "Voice over Internet Protocol". Yahoo! Voice services let you make calls to, and receive calls from, traditional landline and mobile telephones.
The Yahoo! Voice services can only be used if your have a powered-up PC with a microphone and speakers or a headset (plus an Internet connection). The Yahoo! Voice services will not work if you're not connected to the Internet, during any power outages, or if there are any Internet connectivity disruptions.