Gmail, Google Calendar and Google Docs in the mobile browser
These apps are available with a streamlined web interface, where you can easily bookmark a single web address and seamlessly switch between applications. Bookmark http://www.google.com/m/a/example.com from your iPhone or iPod Touch's browser, but remember to replace "example.com" with your actual domain name.
Gmail, Google Calendar and Contacts on pre-installed applications
You can connect to your iPhone or iPod Touch's Mail application to Gmail using Google Sync. Learn more about using IMAP to connect to Gmail here and here about how to configure the iPhone or iPod Touch's Mail application to do this. See below to learn how to get your Gmail pushed directly to your iPhone through Google Sync.
Google Sync now offers two-way synchronization between your calendar, contacts and email on the iPhone or iPod Touch and Google Apps. Updates are done automatically, over the air. Whether you update appointments and contacts from your mobile device or from your computer, you always have access to up-to-date information. To learn how to configure Google Sync for free, visit this help center article, visit this help center article.
Google Talk
You can instant message from your iPhone with Google Talk, too. Bookmark http://talkgadget.google.com/a/example.com/talkgadget/m from your iPhone's browser, but remember to replace "example.com" with your actual domain name.