Skype is a free service providing telephone service over the internet to call anywhere on the planet. (more)

Minimal equipment is required to make calls to other PCs which is known as Skype-to-Skype calling. If you have a PC you can probably Skype. (more)

Optionally, one can purchase usage allowing Skype calls to regular telephone numbers: land-lines or cell - or as it is called, to Skype-out. You can also obtain a telephone number so others can call you. (more)

Skype allows you to hold video-calling and text chats with other Skype users. (more)

There are some accessories which can enhance your Skype experience such as headsets with microphones for your PC, webcams or a specialized Skype-phone. (more)

There is also software which you might find useful such as call recorders. (more)