Just installed an official Skype app on my iPhone 3G through AppStore. The app looks awesome with excellent user experience. It was intelligently designed by keeping usual iPhone habits into consideration, very easy to use, full featured VoIP application.
I liked it a lot even when I am getting crash of app every 2 minutes. I know it will be stable very soon now. Definitely this is one of the most waited app for iPhone platform.
Few good factors:
1. Maintains calls & chats history within iPhone for faster look back
2. You don't need to login everytime you launch it
3. Automatically logs out upon quitting app. Good for battery backup.
4. Can make calls to mobile/landlines using SkypeOut.
5. Best - Make free calls over VoIP using expensive handset :)
6. Yet to test, but it supports conference calls
Skype have finally done it! And it was worth to wait.