There is no such thing as free VoIP calls if you intend to call regular telephone lines. Some services come close and if you are ok with calling other computers only there are some free services.

Most services that tout to be free when calling land-lines, in fact require a deposit or have trial period limitations. Some services give you certain amount of time free, and then start charging when you exceed the threshold, so pay attention to how much time you are using with such services.

If you are only calling another computer, then why even bother with services such as Skype and their Suprenode issues? Simply use Google Talk or MSN/Windows Messenger! Google Talk has a nice web interface not requiring software installation on your machine, great way to VoIP enable any PC.