How can I make a phone call from my mobile phone through gprs to another cell phone?

I have nokia 6600 with gprs connection which connects my laptop to the internet through the bluetooth. Can I make a call to another mobile phone using the gprs internet connection of my laptop just as I make it through the broadband internet? I tried but did not succeed as the connection drops when I dial or there is no voice signal beyond the initial blurred "hallo" from the other side. Any method or software to help please?