This is a step by step guide to setting up Google Sync services on iPhones running Apple iphone OS 3.0. Step by step this is how to link your google calendar and google mail contacts to your iPhone. 2 way syncing is soone yours! Let me know any problems to make this better for us all.
UPDATED to link to steps for Google Apps accounts (New Post)
So, From the home screen, lets goto Settings>
In Settings, touch Mail, Contacts, Calendars >
Touch Add Account > then choose (yes oddly!) Microsoft Exchange
Enter the exchange information shown (substitute user.name in the following screens for your own google account - especially careful if you have a googlemail.com account typically in Europe).
Enter your Email address, press Next, Enter the username and password, Press Next.
Enter the server as m.google.com
This often causes a problem, users are unsure what to do... just click on Accept on the unable to verify warning... Then Next...
Now it will show you the following screen, be sure to Turn Off mail push - Google doesnt support it yet and if you leave it on you will get password errors popping up later...
Ok, we're nearly there, you will see your new account all setup now and your iphone address book will look like the groups screen below.. whilst you're here your iphone is busy talking to the google servers downloading what is needed.
Now if you have multiple calendars, be sure to open Safari on your iphone (this doesnt work from your PC or Mac!) and visit http://m.google.com/sync as shown below. UPDATE: If you have a Google Apps account (not straight forward gmail etc) please follow the steps in this post now.
Sign into your google account...
You may have one device or more (I've tested 3 different iphones recently so have 3 showing.. the only way to distinguish them is the date and time fields though...)
You will then find your calendars that you have setup on the Web Calendar. Be sure to tick the boxes of the calendars you want to sync to your phone...