HOW TO install iCloud on iOS 5 Device
Step 1. Download and Install
Update your iOS device to iOS 5, by downloading iOS 5 beta from the iOS Dev Center. (iOS Developer Program Members Only).
Step 2. Setup Account
Setup your iCloud account either during the iOS 5 setup assistant or by tapping Settings > iCloud and signing in with your Apple ID or creating a new Apple ID.
You can use any Apple ID providing it is a full email address and not a MobileMe account. If you have a MobileMe account, you can copy data from that account to an iCloud account to use during testing.
Step 3. Enable Services
Open the iCloud settings by tapping Settings > iCloud to enable or change the services you wish to use with iCloud