Using Gmail IMAP Application On iPhone 3G
Google has added iPhone to it's list of devices supported by Gmails IMAP Support for Iphone. Gmail is not very spam friendly so most users love it because your mail box doesn't get cluttered with spam.
To add Gmail to your iPhone is easy. We assume you have both, iPhone and Gmail. Receive your Gmail by setting up your email like this. For incoming mail set the server to pull from imap.gmail.com Then enter your user name and password. The outbox should be set smtp.gmail.com
Thats it enjoy Gmail on your iPhone. If you have issues go to this Google
LINK