PC-based telephony is becoming a widely used options for communicating. Internet telephony is the term used to describe a category of hardware and software that enables people to use the Internet as the transmission medium for telephone calls.

For users who have free, or fixed-price Internet access, Internet telephony software essentially provides free telephone calls anywhere in the world. There are many Internet telephony applications available. Some, like Microsoft NetMeeting, come bundled with popular Web browsers. Others are stand-alone products. Internet telephony products are sometimes called IP telephony, Voice over the Internet (VOI) or Voice over IP (VOIP) products. 

Internet telephony can be basically broken down into three categories consisting of PC-to-PC telephony, PC to Phone, and Phone to Phone.

PC-to-PC Calling
PC-to-PC telephonyenables you to call another person who is online at the same time you are, using the same telephony client (or one that is compatible).  To use your PC to talk to another person through his PC, you'll need to have compatible software, a microphone and speakers (or alternatively, a PC headset) and Internet access. While broadband access will work best, you can also make PC-to-PC calls with dial-up Internet access. PC-to-PC telephony is free — you should never be required to pay to make these calls, regardless of where the person you want to communicate is located. PC-to-PC telephony lacks the crisp clear quality that you typically get with regular phone lines, but of course the trade-off is that you won't need to pay to use it, which is why it is a popular communication choice for family and friends who live outside of each other's local telephone calling access.

Today there are myriad software choices, many of them free, which offer basic PC-to-PC calling. It's important to remember that you will need compatible software with the person you are calling, so deciding on a free program before using PC telephony is a good idea. For those who use Instant Messaging programs such as Google Talk, AOL AIM, Yahoo! Messenger or MSN messenger, these communication platforms do have voice communication services built in. Skype, and SharpVoice are other free programs that you can use. Many free PC-to-PC telephony programs also offer PC-to-Phone communications as well. Most PC-to-PC telephony software works like several of the popular Instant Messaging clients. Good PC-to-PC telephony software clients allow you to keep a contact list, and when that contact is online, you simply click to begin a voice conversation, similar to initiating a text instant message. Some clients will allow you to initiate a group or multiple-user PC-to-PC telephony session, while others include this feature only when you upgrade from the free version.

How It Works: The client software converts transmitted speech into data packets and routes it over the Internet. The receiving client turns the data packets back into voice signals that are heard through the speakers or headphones on the receiving end.

PC-to-Phone Calling
PC-to-phone telephony allows you to make calls from your computer to regular telephones. The technology is similar to PC-to-PC calling. While this is a service you pay for, it's usually cheaper than using your long distance telephone provider. To use PC-to-Phone services, you need to have the same equipment used for PC-to-PC calling;  a microphone and speakers (or alternatively, a PC headset), and Internet access.

How It Works: The PC phone user's PC acts as the originating gateway, which converts the voice transmission into data packets onto the Internet. At the end gateway provided by the software distributor, the data packets are converted to voice signals and routed to the PSTN. The PSTN then routes the call to the receiver's telephone, as it would with regular telephone calls.

Phone-to-Phone Calling
A relatively new type of Internet telephony service, which is quickly gaining in popularity with consumers and business. Phone-to-phone telephony also allow telephone calls to be placed over the Internet, but it differs drastically from the other types of Internet telephony. Phone-to-phone telephony does not require users to have special software, or even a computer to use it. Phone-to-phone uses traditional telephones on both ends. To make phone-to-phone telephony calls, you need to have an Internet Telephony Service Provider (ITSP). The ITSP will have gateways in different areas around the world. When you place a call, that call is routed over the Internet to a gateway located the closest to the receiving party. The gateway will then send the call over the PSTN to the receiving party's regular telephone.  Because much of the transmission for the call takes place over the Internet, Phone-to-phone telephony is cheaper than using a regular telephone service provider. Your ITSP will be the one who handles your subscription and billing

How it Works: Users with Internet telephone connections place a call from their landline phone. The voice signals are digitized, compressed and converted to data packets. When the data packets arrive at the gateway, they are converted back into voice signals. Once converted, the voice signals are then transmitted through the local PSTN to the receiver.

 

Vangie 'Aurora' Beal
Writer, www.Webopedia.com
 

SharpVoice
The SharpVoice Network is a Peer-to-Peer Voice over Internet Protocol (VoIP) system that provides clear PC-to-PC and PC-to-Phone communications over a dial-up or broadband connection. It includes client software that you download onto your system and a suite of services that we provide to allow additional services such as buddy lists.

PC-Telephone
PC-Telephone is a communications software application that enables you to use the Internet and public telephone networks ISDN/PSTN. PC-Telephone allows you to make free PC-to-PC calls over the Internet, PC-to-Phone/Fax calls over Internet, and PC-to-Phone/Fax and Phone/Fax-to-PC calls over ISDN.

Net2Phone CommCenter - PC2Phone and PC2Fax Software
Net2Phone CommCenter offers the latest features in Internet technology -- allowing you to place low-cost calls and send faxes right from your computer.

Enterprise VoIP Planet
The IT Manager's Guide to Voice over IP.

The Use of Internet Telephony in Distance & Web based Education
Research by Declan Dunne and Desmond Keegan. By logging onto a computer and putting in the IP address, you can call anywhere in the world and talk to other phone users through the Internet for the price of a local call to your Internet Service Provider (ISP).