Syncing your iphone or ipad with google: Here are the detailed instructions on syncing your iphone or ipad with google gmail calendar and contacts.
After doing this you will have all your google contacts on your iphone or ipad, and all your google calendars on your iphone (or your ipod touch) – any changed you make on google, or on your iphone will be ‘saved’ to your google contacts / calendar.
Now when you open the Calendar app on your iPhone or iPad, you’ll see your Google Calendar events.
If you have more than one calendar set up in Google Calendar on the web, you can choose which calendars to sync:
Go to www.google.com/calendar/syncselect.
Check the boxes for the calendars you want to sync.
In the bottom right corner, touch Save.
You will now have your gmail account, your google calendars and you will have all your contact on your iphone / ipad / ipod touch! –
If you have done all this then you will have the same list of contacts on your mac, on your iphone, and on your google contacts. you will also have the same calendars. any change, or addition you make on any device will show up in all the others
sources: google calendar support