Source: http://feeds.feedburner.com/~r/lifehacker/full/~3/411223942/make-skype-calls-with-fring-on-your-iphone
iPhone 2.0 only: Free application Fring puts popular chat applications on your iPhone, including Skype—and the ability to make Skype voice over IP calls when your phone is connected to a Wi-Fi network. Fring puts all your chat buddies from AIM, MSN, Google Talk, Yahoo, ICQ, Twitter, and Skype on your iPhone, and lets you know who's online when. Chat your buddies whether you're connected via data or Wi-Fi, and make Skype calls (or Skype Out calls) when you're on a local network. Fring is a free download for iPhones running the 2.0 software.