Previewed at WWDC, launching in the fall.
Google Adds Push Gmail for iPhone and iPod Touch Via Google Sync
When we launched Google Sync for Contacts and Google Calendar earlier this year, an over-the-air, always-on connection to sync mail was noticeably absent. We heard your requests loud and clear, and starting today you can use Google Sync to get your Gmail messages pushed directly to your iPhone, iPod Touch, or Windows Mobile device.
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 If your software is out of date, follow Apple's upgrade instructions.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.