Push mail is now supported on iPhone and Windows Mobile devices using Google Sync!!!

Editions included:
Standard, Premier, Education and Partner Editions

Languages included:
US English

How to access what's new:
Administrators first need to enable Google Sync in the administrator control panel under 'Mobile Settings'. If you're already using Google Sync for contacts and calendar, push mail is automatically enabled but you may need to switch it on on your device.

Click here to get the instructions on how to set up Google Sync on an iPhone.

Click here to get the instructions on how to set up Google Sync on a Windows Mobile device.

For more information:
http://googleenterprise.blogspot.com/2009/09/push-mail-for-iphone-and-windows-mobile.html