We’ve been desperate for a centralised calendar solution that can sync with all our desktop PCs and iPhones for a while now, and yesterday one of our developers, Matt, found a solution for us.
It combines the following technologies:
Essentially Google Calendar is used to provide a central calendar, this is then synced to the iPhones via Nuevasync, which provides a free exchange interface. The calaboration tool makes it easy to sync your iCal with the Google Calendar, and then MobileMe is needed if you want to have a private calendar on your iPhone as well.
Matt has written some in-depth instructions on how to set up over the air calendar syncing on your iPhone, over on his blog.