Hi there,
First off you dont NEED software, you can actually just use a VoIP handset the plugs directly in to your broadband box - no PC needed.
If however you want to go down the PC route, in order to use some of the basic services, you can probably get away with just your PC, an internet connection, and your speakers/microphone. Most feel that using a headset is a much better solution. Speakers will often produce feedback.
In general, you need:
A high-speed internet connection. This can be a cable modem, or a super high-speed services such as ISDN, DSL or a T-1 link. The link you choose will depend upon the amount of telephone traffic you intend to use. A typical DSL link, for instance, is enough for eight simultaneous phone calls.
An account with a VoIP provider. Your account can be configured to recognize your calls automatically, or you can require your users to enter their unique account numbers, issued by you.
A "softphone". A softphone is a multi-media application that works in association with VoiP technology enabling you to make calls direct from your PC or laptop. Appearing as an image of a telephone on your computer, it can be downloaded from many suppliers such as Xten -
http://xten.com
Hope this helps!
Matt

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