To use MobileMe on iPhone, you need to set up a MobileMe Free Account or a MobileMe Paid Subscription.
A MobileMe Free Account lets you use Find My iPhone (not available in all countries or regions), a feature that helps you locate and protect the information on your iPhone if it’s lost or stolen. See Security Features.
A MobileMe Paid Subscription lets you use Find My iPhone, plus the following features:
Mail account at me.com
Over-the-air syncing for contacts, calendars, bookmarks, and notes
MobileMe Gallery for sharing photos and videos
MobileMe iDisk for storing and sharing files
You can try out these features with a 60-day free trial at www.apple.com/mobileme.
A MobileMe Free Account is available to any customer with an iPhone 4 running iOS 4.2 or later. If you’ve already created an account for the App Store or Game Center, you can use that Apple ID for your MobileMe Free Account. You can create a new Apple ID if you don’t already have one, or if you want a different Apple ID for your MobileMe account.
Set up a MobileMe Free Account:
In Settings, tap “Mail, Contacts, Calendars.”
Tap Add Account, then tap MobileMe.
Enter your Apple ID and password, or tap Create Free Apple ID.
Follow the onscreen instructions.
Verify your email address, if required.
Make sure Find My iPhone is turned on.
Only one MobileMe account at a time can be used for Find My iPhone and for syncing contacts, calendars, bookmarks, and notes.
To use Gallery, iDisk, and Find My iPhone on iPhone, download the free MobileMe Gallery, MobileMe iDisk, and Find My iPhone apps from the App Store.