Yes and no. You only get charged minutes when you call from Skype to a NON-SKYPE USER (ie, landlines, mobile phones). You don't get charged when you call another Skype user.
I wouldn't call it useless. I've been able to talk to friends abroad (Skype to Skype) for free*
*I mean, you pay for the phone service and the data package but that's it, you don't use your minutes... just data which is unlimited.