Coming from another platform where you're used to the Gmail app on Android or the instant push of BlackBerry mail and curious how to get that on your iPhone? Well good news -- Google licensed Exchange ActiveSync from Microsoft and offers Google Sync for iPhone (and other devices). So if you set up your Gmail (or Google Account) as an Exchange account you get push email, calendars, and contacts.
WARNING: Your iPhone will ask if you want to delete all existing data and replace it with Google data, or merge the two. What you choose depends on how you store your data. If everything is in the Google Cloud, choose replace. If you have a mix of data from, for example, Outlook as well, choose merge.