Free calls to the UK

This weekend, Skype are doing free calls to the UK, to normal phone lines. All you need to do is download the program and sign up for it (free also). From what i know of it, its an MSN style program, but allows you to call normal phones as well, usually for a small, pre-paid fee.
I plan to use this to call home when we move, as im guessing its cheaper to use than standard hard lines.