Google Sync is a service from Google that keeps your phone’s native mail and calendar apps in sync with your Gmail, Calendar and Contacts.
An update to the service today has added three new features;
1. The ability to search all emails on Gmail, not just locally stored mail by iOS mail app.
2. Ability to send mail from a different account other than Gmail.
3. Accept, edit and decline calendar events from the iOS calendar app.
Both Gmail and Google Apps email users will benefit from these updates. You can follow this guide to set up Google Sync for your iOS device.