FnF Dialer is an old application that seems to be discontinued and replaced by Call to FnF dialer. In order to use it, you need to install the software on your computer, to purchase a credit card from a local reseller and to configure your security program and Windows firewall to allow the application to communicate. Also, if you're living in Oman, Bahrain, Belize, Yemen, China, Jordan, Kuwait, Iran, Malaysia, Libya, Thailand, Syria or Pakistan you can't use the software because these countries blocked the VoIP services. For further information I suggest you check the official web page.