The call (skype to skype) is free. But the internet connection for your mobile isn't. Not unless you can connect through a free WiFi connection. Then, both of them would be free...
Hiya Micky! Im hooked up to 3 Mobile using my N95/8gig handset,the Skype application is installed free of charge! You can only ring those using the same service! And its free to use worldwide!