
Skype calls between computers are free. Calls from a computer to a normal phone or mobile are charged at low rates, for which you have to buy credits. This service is called SkypeOut. You can also buy a Skype phone number (30 Euros/yr) which allows people to call you on your computer. This can be useful as it means you can take phone calls on any computer anywhere in the world. This service is called SkypeIn.
Biggest user base by a long way
Owned by eBay so will continually be improved
Very easy to use
Uses a lot of YOUR computer processing power even when you are not making calls
Call quality poor at busy times
Has had reliability problems
Skype@ Skype.com