This leaves you with the following alternatives:
- Mobile Me: Allows you to sync your iOS device over the internet and provides a web application to manage the calendars. Pro: I’ve heard good things about the web application. Con: Costs.
- Microsoft Exchange: You need an exchange server. I don’t know more about this solution, so I cannot comment on pros and cons.
- Google Calendar: There are several ways of syncing your Google Calendar account with iOS. Pro: free, nice web app. Con: You depend on Google which is often slow to fix bugs and completely shuts itself off from customer requests.
- Google Sync: Allows you to sync your Google Calendars as an MS Exchange account.
[Old, does not work any more, all calendars are always synced] If you want to sync more than one calendar, you need to configure this via Google Sync at http://m.google.com/sync/ Warning: works only from an iPhone. On other devices, you need to fake the iPhone as the browser user agent.
- Google Calendar CalDAV: Uses the CalDAV protocol for synchronization. By default, only the default calendar is synced, if you want to synchronize multiple calendars, you need to configure this via www.google.com/calendar/iphoneselect (source: Google).
- Calengoo: Is an app for the iPhone/iPad that directly accesses Google Calendar and also works offline. Has a nice user interface, many people seem to prefer it to the built-in calendar. Con: Costs.
- (1) and (2) are compared in a thread on Google’s support forums. Summary: Google Sync is currently better (uses less battery, does push).
- Calendars that you sync between your PC/Mac and iPhone/iPad can be unsubscribed either before or after adding the calendars from Google Calendar. In the latter case, don’t remove anything existing when adding the new data (there is an option to do so when adding an account). In either case, iTunes offers you to remove the calendars from your iOS device when you unsubscribe.
- iCal/Sunbird: CalDAV.
- Outlook: Google Calendar Sync.
- Mac-only: BusySync (bought it in pre-CalDAV times, works really well). Pro: You only pay once.
- Mac-only: Spanning Sync. Con: Yearly subscription.