Skype-to-Skype calls are free. It doesn’t matter where you are in the world, or where the person you’re calling is. It doesn’t even matter if you’re using Skype on a computer, mobile phone or tablet*. As long as you’re both using Skype, the call is completely free.
You can make Skype-to-Skype calls using video or just voice – it’s up to you. Make a voice call with up to 25 people at once and that’s free too (as long as everyone’s on Skype). If you want to have a video call with more than two people, that's also free.
* WiFi connection or mobile data plan required.