To enable Gmail with Push Email on an iPhone follow these steps.
Open the "Settings" application go to "Mail, Contacts, Calendars" and click "Add account...";
|iPad: "Add Account" Under Settings|
|iPad: Add An Exchange Account|
|iPad: Add An Exchange Account (completed)|
|iPad: Add an Exchange Account With Server|
Your account will now be verified by Google and providing you have entered everything correctly you will then be presented with the option what to sync with your device;
|iPad: Select Items To Sync|
When you're done click "Save" at the top right and you'll now have Push Email on your device.