GigaOm reports that their sources tell them that Skype will be coming to the iPhone as early as next week. Update: Skype for iPhone is official.
Given that you can already use Skype VOIP on the iPhone with for instance the Fring App (site), the rumor is not that exciting.
A Skype iPhone App will though bring more visibility to the fact that you can use VOIP on your iPhone. Just make sure you have a nice data plan.