A brief technology lesson will help you understand where telephone service has been and where it's going. Digital telephone service is delivered over the same networks in much the same fashion analog calls are. That is, they're transformed into small bits that can be more efficiently transmitted over a network. Digitizing a signal reduces the noise pollution that can infect a telephone call. When the call reaches its destination, all of its packets are reassembled to create the finished product.
Packetized calls are cheaper than calls sent over the established telephone companies' networks.
The companies also require a short registration form, as well as a credit card account so you can be billed for your calls. When that's done, you'll be able to place a call from your PC to another user's telephone with a few mouse clicks. As with any new technology, digital and IP telephony service providers must work out some bugs. If a call is missing some pieces at the end of its journey, that call's sound can be scratchy or barely audible. Offering such features as caller ID and call-waiting to consumers spoiled by decades of strong Baby Bell service is a challenge.