Google-hosted mail accounts are now fully accessible via Exchange Active Synch (EAS).  This means that Google-hosted email users (e.g., gmail.com and sterndata.com) now have push email enabled for the iPhone.  All that's required is setting up the account as a Microsoft Exchange account rather than Gmail.  There's no free lunch -- push email tends to eat your battery a little bit faster.

If you have another type of smartphone, Google has instructions here.

Step 1, create a new mail account as Microsoft Exchange.

Step 2, fill in your stuff

Step 3, enable features and choose which mail folder gets pushed