2-Way Sync - Google Calendar (Gcalendar/Gcal) and iPhone

It can be done, and I've tested it! These instructions are for an iCal-enabled computer (specifically a Mac). It does require:

• MobileMe ($70 if you get it with a new iPhone, $100 otherwise; or $120/150 for a family plan, for 5 people) - this syncs your iPhone to iCal
• Spanning Sync - syncs your Google Calendar(s) to iCal

I suspect Google will eventually come up with an iPhone App to replace Spanning Sync, but MobileMe will most certainly be an essential part of the equation.

Here's how it works.

Centralize your Google Calendars through one account's calendar. So, if you have your own personal Google account (your "centralized" calendar), plus a few others, including a Google Apps calendar for another domain (your "satellite calendars"), then go to each "satellite" calendar and:

1. go to Settings > Calendars
2. click the Shared: Edit settings link
3. add, under "Share with specific people", the email address associated with your "centralized" calendar, and set the permission to Make Changes AND Manage Sharing. (If you can't do the latter, make sure your domain's admin changes settings to allow this option. Here are the instructions)

Now, in your "centralized" calendar, you should be able to see all the other calendars' items if you highlight those calendars under the Other Calendars box to the left.

Go to me.com and set up a MobileMe account. You'll get an @me.com email address and an associated password.

On your primary computer (note: this computer must stay on for the over-the-air syncing to work, once you've gotten everything set up), install MobileMe by:

1. Updating your computer with all the new Apple software (my computer is only 3 months old and the total download was over 100MB, and took about 30 minutes, including a few restarts - don't worry!)
2. Go to System Preferences and choose MobileMe under Internet & Network
3. Under the Account tab, sign in using your MobileMe credentials.
4. Click the Sync tab, set it to Synchronize with MobileMe Automatically, and check off the items you want to synchronize (at the very least Calendar)
5. Click the Sync Now button if you like.

On your Mac:

1. download and install Spanning Sync.
2. Open System Preferences, and under Other, click Spanning Sync
3. log into your "centralized" Google account
4. Check the Home and Work calendars, and choose which Google calendar you want them to sync with.
5. Specify how often you want the Sync with your Google Calendars to occur (anywhere from 10 minutes to every week, or manually). I choose every 10 minutes because these are all hosted services so there's no battery power drainage issues.
6. Hit the Sync Now button, if you like.

On your iPhone:

1. Click Settings (same icon as your Mac's System Preferences)
2. Click Fetch New Data
3. Enable Push by switching to On
4. For non-pushable stuff, specify how often you want your iPhone to fetch (for example: my work email doesn't allow Push for whatever reason, but you can go down to Advanced and set each mail/calendar/contacts account to Push or Fetch)
5. back out to Settings again
6. Click Mail, Contacts, Calendar
7. Set up (if it's not there already) your MobileMe account by clicking Add Account...
8. Choose the pretty MobileMe icon
9. Enter in your MobileMe signin credentials and hit the Save button
10. Click your MobileMe account under Accounts (should be your @me.com address)
11. Switch, at least, Calendars to On
12. Back out

You should be set! Test it!

Set up a dummy appointment in one of your "satellite" Google Calendars, and watch it migrate through your "centralized" Google Calendar, then to your Mac's iCal, and then to your iPhone.

Then delete the appointment on your iPhone (or move it to a different time), and watch it back-migrate to your "satellite" Google Calendar.

It works, although it's limited to the sync intervals you set up. Spanning Sync is the only enforced bottleneck (so a minimum of 10 minutes); the rest can be set up to push automatically, but, you can, for example, set MobileMe to sync every hour instead of automatically, in which case it would set the syncing interval.