From Voxalot FAQ

What is VoxCall

VoxCall is an exciting new initiative from Voxalot that allows facebook users to click on their friends and initiate phone calls. The beauty of VoxCall is that it is self-organising in that if your VoxCall friend changes their contact phone number, you don't even have to be notified... VoxCall will use whatever number they have registered.

A list of VoxCall "friendly" providers, communities and applications can also be found on our VoxCall Compatibility page.

How does it work

The underlying technology that VoxCall uses to connect calls is Voice over IP addresses (often known as SIP URIs). When you add the VoxCall application, you will be prompted to enter your SIP URI. To ensure that you are the rightful owner of that number, VoxCall will display a PIN number on the screen and then call the number you entered. Your phone will ring and you will be prompted to enter the PIN, which is validated. Once Validated, you are now ready to use VoxCall! Congratulations.

When you click on a VoxCall friend, your phone will be called by VoxCall. When you answer, VoxCall will dial your friend and connect them to you. Easy as 1,2,3!

And the beauty of VoxCall and VoIP is that it is all FREE!!

What if you don't have a SIP URI?

Do you want to be able to have people call on your landline or mobile number? VoxPremium is just what you need! Among other things, VoxPremium allows you to forward a SIP URI to a land-line or mobile phone number by using the Voice Service Provider of your choice(*).

It is a simple 3 step process:

1. Sign up with a Voice Service Provider (VSP) of your choice. If you don't know who you should sign up with, you can use our Global Provider List to find one that is near to you. A list of VoxCall "friendly" providers, communities and applications can also be found on our VoxCall Compatibility page.
2. Register for a VoxPremium account for only USD$15 per year.
3. Enter your VSP details in the Providers page, and create a Call Connection rule to forward all calls to your home phone number (or work number, or mobile, ...)

And that is it. You can now register your Voxalot SIP URI in VoxCall and be reached wherever you like.

There are many other benefits of VoxPremium that you can enjoy such as being able to create additional rules that forward to voicemail at certain times, block specific inbound numbers, etc.