PilotLog
I started using this program as soon as I got the iPhone. The guys gave me enough free time, so I could fully evaluate it against my previous PalmLog Pro.
I took my time - 3 months. I import my roster and then can download an ical file, that synchronizes with the Calendar. It's a fantastic tool.
Cost is 5 GBP/month or 50 up front.
Cheers