Skype uses their own proprietry system. It works well, is generally good quality and is Free!
Calls to other skype users are free, calls to land lin phones are chargeable (you have to add credit before you can make land line calls).
The software is a free download, all you need is a PC (Toughbook) with mike & speaker.
Magicjack is (I believe) also a proprietry gadget and protocol. It allows normal phones to be connected rather than using the PC mike & speakers.
The general name for any voice-over-broadband system is VoIP - Voice over Internet Protocol.
The commonest standard system is SIP - this is supported by numerous providers and masses of hardware and software.
You can get cheap and free accounts that allow incoming & outgoing calls to the 'normal' land line & mobile phone system
I use a provider called Sipgate, who give you a free incoming land-line number (called a DID, direct inward dial), and outgoing calls at a relatively low cost. I connect to them with a software PBX telephone exchange (Asterisk) which has several extension phones and also connects to my normal land line.
Another one is 'voipstunt' who give you a few hours a week of free calls to just about anywhere in the world for a subscription cost of a few dollars a year.
They have their own software phone which you must use to create the account, but then you can use the login info with any generic SIP software or hardware device.
There are many, many more.
You can get a little box that connects in line with a normal phone, plus an ethernet link to your broadband internet. This is set up via a web browser and connects to a SIP account on whatever provider you chose.
You can then make and receive calls both by your normal phone company and via the internet service using your normal house phones & no computer needed.
An example of one of these is a Sipura / Linksys SPA3102
You can do some neat tricks with combinations of gear..
My mobile (Nokia E65) has both built-in WiFi and a SIP client.
This is configured to connect to my PBX when I'm in range of my home network, and it then also acts as a cordless extension to the landline phone, while still also accepting mobile calls.
Another thing you can do is get an account with the incoming number in another country - so friends or relatives there can call you without an international charge. You can also do this for another city if it puts the number in a 'free local calls' zone with someone..
For more info, have a look at these sites:http://www.asterisk.org
- incredibly powerfull software phone system (that uses horrendously complex text config files).http://www.freepbx.org
- web based configuration & control system for asterisk that makes setup a doddle and adds many facilities.http://www.voip-info.org/
- site that lists just about anything in any way connected to VoIP stuff, and has lists of providers of cheap & free DIDs on various countries.