Here are the detailed instructions on how you can sync your iphone / ipod touch / ipad with google / gmail / google calendar / google 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.
you will now have your gmail account, your google calendars and you will have all your contact on your iphone / ipad / ipod touch! -
please see this post for details on how to get your google calendar synced to your ical on your mac
and this post on how to sync your addressbook with your google contacts
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