Push Gmail for iPhone and Windows Mobile

Google launched Google Sync for iPhone and Windows Mobile phones to support Over the Air (OTA) Push Email/Contacts and Calendar.

You can set up push Gmail by itself or choose to sync your Contacts and/or Calendar as well. If you're using an iPhone, make sure you're running iPhone OS version 3.0 or above (on your device, click Settings > General > About and scroll down until you see Version). If your software is out of date, follow Apple's upgrade instructions. Then, visit m.google.com/sync from your computer for set up instructions. If you're already using Google Sync, you can just enable push mail.

For more information visit:
http://gmailblog.blogspot.com/2009/09/push-gmail-for-iphone-and-windows.html