MagicJack was invented by Dan Borislow and launched in late 2007. Both the original MagicJack and the newer MagicJack Plus are analog telephone adapters (ATAs), roughly the size of a matchbox, that allow you to make VoIP phone calls over your Internet connection. The original has a USB connector and a standard RJ11 phone jack. The newer MagicJack Plus has both of those plus an Ethernet port, and it incorporates its own motherboard, removing the need for a constant computer connection.
To use the original MagicJack, plug the device into your computer's USB port and it automatically installs software on your computer. Once setup and registration are complete, you plug a corded or cordless phone into the phone jack and you should be ready to make and receive calls. You can even dispense with the physical phone and use the MagicJack soft-phone (software phone) to dial numbers via a virtual keypad on your screen and talk directly via your computer's speaker and microphone or an attached headset. This version requires that your computer stay on and awake constantly to make and receive calls. If you turn off your computer or it goes to sleep, you can still get voicemail, and call forwarding will still work.
To set up the new MagicJack Plus, you still need to plug it into a computer and go through several setup and registration steps. After that, you can either use it like the original -- via your computer -- or plug the device into your broadband modem or router via an Ethernet port (the cable is included). This arrangement will require you to connect a phone and to plug the device into an AC power adapter (also included). The main advantage over the original is that your computer does not need to be present, let alone turned on all the time, for you to make and receive calls. But as with original MagicJack, broadband is required.
MagicJack Plus is compatible with Windows XP, Windows Vista, Windows 7, Windows 8 and Intel-based Apple Macintosh OS. The original silver MagicJack is supported on all of the above except for Windows 8. Linux and non-Intel Mac users are currently out of luck with both versions.