The first question is why would you want to set up Microsoft exchange for Gmail over the built-in Gmail option? The advantage to using Microsoft exchange, is that it has Push services. Push is a not so fancy way of saying; when an e-mail hits your Gmail account, it is immediately also pushed to your iPhone, so instead of checking periodically for new mail every 10 minutes, you get it asap.
Using exchange you also have the added advantage of syncing your Gmail contacts, so you have a backup for when you need it. It’s actually pretty straight forward (and free) to do this.
Before you continue, you need to have least iOS 3.0 to set this up. Back up all your iPhone settings, and sync before you start this process. Always nice to have a backup in case things don’t work out!
1. Open the settings app, and navigate to Mail, select ‘add an account’.
2. Instead of ‘Gmail’ select ‘Microsoft Exchange’.
3. Enter the details, as requested. Type in your Gmail e-mail address. Leave domain name blank. Type in the username, which is your FULL email address, and also type in your password. You can also enter a description if you wish. Select Next.
4. When the screen reloads enter the server address “m.google.com”. Tap next.
5. You can now select what you would like to sync. iOS 5.0 will allow you to include reminders, when it launches later this year. Make your selection and press save. You may be asked some sync questions if you already have iPhone contacts, make sure to select “Keep on my iPhone” unless you want those deleted.