If you have an iPhone with OS 3.0 or greater and Exchange 2007 it will require you to enable a PIN on your device by default. To disable this you need to...
- Open the Exchange Management Console
- Expand the Organization Configuration
- Click on Client Access
- Double click your Activesync Mailbox Policy
- Click the Password tab
- Uncheck Require password and click OK
If your iPhone is already syncing with Exchange you'll need to remove the partnership for the setting to take effect.
- In the console tree, navigate to Recipient Configuration > Mailbox.
- Select a user, and then select Manage Mobile Device from the action pane. * The Manage Mobile Device dialog box will display a list of all devices that are configured for synchronization.
- Choose the device, Select Remove mobile device parternship and click Remove.
Note: The Manage Mobile Device link is only available in the action pane for users who've established a mobile phone partnership with the Exchange server.