How to enable Entourage syncing to iPhone
Microsoft Entourage 2004 is one of the applications on a Mac that you can sync contacts and calendars with iPhone.
Entourage contact and calendar syncing requires the Microsoft Office 2004 for Mac 11.3.5 Update, accessible here. or you can use the Microsoft AutoUpdate application.
The Entourage MVPs have more information here.
Finally, last year I did a video for Sync Services in Entourage that you might find useful. The UI for iTunes is now different, but you'll get the idea:
Video: Sync Services in Entourage