Skype is the world's leading VoIP calling service. A free tool that lets you talk to other users using text chats, voice and/or video conversations.

The tool uses a peer-to-peer technology based on the well known file exchange service, Kazaa, to offer a robust and trustworthy call system, allowing you to talk to your friends with the same reliability and sound quality you would expect on a landline phone.

It uses VoIP technology to make calls between users and calls from its users to regular phones, both mobile and landline, all in a very simple and quick way that doesn’t require you to set-up or configure anything. Its creators affirm that it even offers an audio quality that’s better than that on a regular phone call.

It’s completely free and comes with no extra ads; you'll hear the typical dialing phone sounds, it'll tell you if the contact you are calling is talking on Skype at that moment, and you can pick up and hang up all the calls you want.

Plus, it includes Facebook integration and the option of making group video-calls with up to ten users at a time using their webcams; not to mention that it includes the Windows Live Messenger messaging after having been purchased by Microsoft.

As it’s a multiplatform application, you can make calls between devices, whether they're your desktop or smartphone. Skype is, quite definitely, one of the leading digital VoIP telephone services in the world.