From the Manufacturer
The magicJack uses your computer and Internet service so you can make local and long distance calls in the U.S. and Canada with no monthly bills. First you connect any household phone to magicJack. Then you plug magicJack into an available USB port on your computer, using the supplied extension cord if needed. Finally you wait for the completion screen to appear to use your phone like you always have. Installation is simple and takes 60 seconds.
Add magicJack Telephone Adapter to your PC and you can make telephone calls within the USA and Canada for FREE! Skype uses a peer-to-peer network, whereas magicJack uses a dedicated telephone networkOther VoIP carriers do not have dedicated telephone networks, and lease this service from other companies. That means higher costs and poorer reliability. magicJack uses its own dedicated telephone network. You can use magicJack with either a regular telephone handset, or with a headset. You can also use both, and switch between the two. You can move magicJack between Internet providers. You can use magicJack from anywhere in the world (where broadband web access is available). It requires - PC - Windows XP or Vista operating system; (Mac/Apple expected soon); Broadband, high-speed internet, cable internet, DSL - WiFi - WiMax magicJack comes with an easy-to-use device to allow you to use a regular telephone handset. Service is free for 1st year. $20 per year thereafter.