This is very cool. We were having this conversation the other day and sure enough, @ginatrapani shared this three month old post on twitter today and it was PERFECT timing! I love it when it works like that. This is super easy to set up.
note: One thing you wanna be careful about though is the duplication or deleting of contacts and calendars.
Steps from the post itself:
Open up the Settings app on your iOS device and go to the "Mail, Contacts, Calendars" section. Hit "Add Account".
From there, choose Microsoft Exchange as the type of account (again, don't choose Gmail).
Type in your Gmail address under Email. Leave the Domain field blank and enter your full Gmail address under Username (including the @gmail.com, @googlemail.com, or other suffix). Type in your password and give it any description you like. Mine's just called "Gmail".
Press the Next button at the top of the screen. It should pop up a message saying Unable to Verify Certificate—if it does, just hit cancel. Then, type m.google.com in the new "Server" box that shows up at the top of the screen. Then tap Next.