The new iPhone iOS 4 is now available for download. There are so many great new additions to the new operating system. I'm particularly loving multitasking, app folders and an integrated inbox for mail. iOS 4 also offers 2 Microsoft Exchange accounts (it was limited to just 1 until now). If you have an office email account using Exchange and a Google account there was no way to have both on Exchange. This meant that you couldn't have your email accounts, calendars and contacts integrated. In theory, having 2 Exchange accounts should just work. However, after attempting to get them to work I realized it was best to stay with one Exchange account for the office and continue to use Gmail over IMAP.

One great thing about Gmail on the iPhone in iOS 4 is that when you add a Gmail account from the Settings > Mail, Contacts, Calendars > Add Account... > Gmail it defaults to IMAP assuming you've configured your Gmail account to be IMAP. Previously you had to add an IMAP Gmail account by going to Other. No longer! If you do it this way do not select the option to sync your calendars. We're going to use a more reliable method later. But first things first: enable IMAP.

Enabling IMAP in Gmail

You'll first need to make sure your Gmail account is configured for IMAP. Following the instructions at http://mail.google.com/support/bin/answer.py?answer=77695 we get:

1. Sign in to Gmail.
2. Click Settings at the top of any Gmail page.
3. Click Forwarding and POP/IMAP.
4. Select Enable IMAP.
5. Configure your IMAP client and click Save Changes.

Syncing your Google calendars with the Calendar App

All of you Google calendars, even those shared with you from other people, can be accessed through your Calendar App if you've configured it correctly. To get your Google calendars to show up you'll want to add them via CalDav. Following the instructions at http://www.google.com/support/mobile/bin/answer.py?hl=en&answer=151674 we get:

1. Open the Settings application on your device's home screen.
2. Open Mail, Contacts, Calendars.
3. Select Add Account...
4. Select Other.
5. Select Add CalDAV Account.
6. Enter your account information:
   • In the Server field, enter [ google.com ]
   • In the Username field, enter your full Google Account or Google Apps email address.
   • In the Password field, enter your Google Account or Google Apps password.
   • In the Description field, enter the name you'd like to appear on the account.
7. Select Next at the top of your screen.

After you've completed setup, open the Calendar app on your device and syncing will automatically begin.

By default only your primary calendar will be synced to your device. You can sync additional calendars by visiting the following page from any web browser:

• https://www.google.com/calendar/iphoneselect

This is an important step. You might even want to do this first.

Note: One thing I noticed was that not all of the colors matched. Even after following the various tips here I was unable to get my primary Google calendar's color to match on the website and on my iPhone. In the end I just made the color on the website match as close as possible to the color that was being set for it on my iPhone so they were at least the same.

Adding other calendars like US Holidays

Even though I have US Holidays in Google Calendars there's no way for that calendar (or the Weather Calendar) to by synced with the iPhone Calendar App. To get around this I added Apple's iCal US Holiday calendar. Following the instructions at http://www.knowyourcell.com/apple/apple-iphone-4/iphone-4-guides/506391/how_to_add_us_holidays_to_your_iphone_4_calendar.html we get: 

1. Open the Settings application on your device's home screen.
2. Open Mail, Contacts, Calendars.
3. Select Add Account...
4. Select Other.
5. Select Add Subscribed Calendar.
6. In the server field, input: ical.mac.com/ical/US32Holidays.ics - then select Next.
7. Select Save.

After following these steps you should now have all of your mail accounts in one inbox and all of your calendars in your Calendar App.