It is called “Fring” (and it is now an accepted terminology to use the word “fringing”!).
It not only allows you to make Skype calls and do Skype chats, but also integrates with MSN Messenger, Google Talk, Twitter and a whole lot of other chatting services.
Check out the Fring site for more.
Installing it was a breeze. And the interface is really nice and simple. It uses WiFi to make Skype calls. So if your phone is connected to WiFi, you can make Skype calls.
Fring is also available for other handsets like Wi-Fi Symbian 8 or 9, Windows Mobile 5 or 6 and UIQ.