We also have a conference call feature where up to five people can talk on one Skype call.
What we are doing is taking advantage of the broadband Internet to provide basically unlimited free calls to anyone at a higher voice quality than they can with the phone lines.
Yes the calls are free. But you're paying for the mobile access and that drives usage and something that drives usage is good for the operators.
At the office, we actually don't have a land phone line. We use Skype mostly, and mobile phones to receive calls from people not on Skype.