Earlier in 2013, Google killed "Google Sync" for non business customers. This allowed an iPhone user to login as an Exchange account on the iPhone using a Gmail account. When they offered the replacements of CalDAV and CardDAV, it was still possible to sync this information to an iPhone. CalDAV was built into the Gmail setup process on the iPhone, but CardDAV was not. It required an additional setup step to make it work. This has changed in iOS 7 and it will be an option when you add a Gmail account.