Skype is VoIP Limited To Free Use With Other Skype users.

Skype is a free voice over internet utility that allows anybody with a computer and Internet connection to call anyone else who also has Skype enabled at no cost (other than the cost of your local Internet call). The Skype software is free, and the calls are free.

The big drawback with free Skype is that you can only call friends and others who have a similar free Skype account ... you cannot call anybody else

Skype make money by selling services supporting VoIP or voice over internet like USB plug in phones that enable you to call anybody. In this case the system is not free.

A  Skype and it software Skype Mate integrates with Skype itself. Pick up the telephone handset, and the Skype PC Phone pops up. You can scrolol for contact numbers and then dial. You will hear the connection being made. Speed dial can also be set up.

Incoming calls ring on the PC phone and show the caller's Skype ID. Once the call is connected, you can choose between the phone handset and using the speaker phone.