IPhone – How to sync the Google calendar with the iPhone

Spanning Sync ($25/year) should do this. However, when I tried to use it I kept getting a crash (version 3.2/443).

BusySync ($39.99) should also do this [edit: I just got a note from BusySync support saying that this does not work for Exchange].

You may now add and edit events, in iCal or Google, on any of the calendars you published or subscribed to, and the events will sync in both directions between iCal and Google.

However, when I set up my Exchange calendar to publish to Google, and modified the calendar inside the Google Calendar interface, the new modifications get clobbered the next time BusySync syncs. It does at least successfully publish the events on Google Calendar, though.

With iCloud, you can choose which areas to sync and which not to. However, if you do choose to sync contacts and/or calendar, I believe you will simply end up with some double events on your phone, which can easily be cleared up by disabling view of the extra calendars.

In short, syncing contacts, calendar, music, and photos are all separate and can be enabled/disabled as such.

And yes, it does, in some way offer you additional redundancy as the Apple cloud and Google cloud are likely housed in different data centers...but this would require you to keep both calendars in sync, which I don't think will be easy to do without being annoyed absurdly.