"Lets you make calls from your PC between users from any continent."
These days the use of traditional landlines is diminishing. Many homes don;t even have one and rely solely on mobile phones. But they are costly to make long or long distance calls with. Instead you could consider a program like X-Lite 3.0. As you might be able to gather by now, X-Lite 3.0 is a softphone that lets you make calls from your computer between users from any continent. You can also send multimedia elements, music, videos and even a personal agenda.
X-Lite 3.0 combines voice and video calls in a user-friendly interface. It also offers instant messaging facilities, contacts lists which you can organize into categories (Work, Family, Friends, etc), and you can see your call logs. It works with most networks by offering Open Standards and Session Initiated Protocol (SIP) based call signaling. It even offers voicemail and is very simple to download, install and configure. You will soon be up and running and be able to see who of your contacts is online.
In X-Lite 3.0 the user only has to register and then will have their own IP number (VoIP) to make calls to anyone on the softphone network.