The WiFi is just to get Internet access. It doesn't involve Skype. The cost is between you and whomever supplies the Wifi "hotspot". It could be yourself as you use your own WiFi-enabled home router. It could be your employer as you use the company's WiFi router. It could be Starbuck's WiFi router or the WiFi router at the executive lounge at the airport. The Skype software client could be on your home desktop PC, on your laptop PC, on your iPhone, or on your Android smartphone, or on a WiFi cordless phone. That software client then calls Skype over the Internet to establish an IP connection for voice data packets to flow over the Internet between itself and other software clients.
"Skype WiFi", OTOH, is a way to pay for that WiFi Internet access by using Skype credits to pay WiFi providers who have signed up as Skype Partners, and the Skype WiFi app makes connecting to the hotspot a simple single click. It's pretty expensive, though, at about 14 cents/minute. Here is a URL of the screen shot of the iPhone Skype WiFi app:
When the app is running and it's within range of a Skype WiFi hotspot (Boingo in this case), the offer pops up and you can click to connect via Boingo's WiFi service.