New evidence uncovered in recent iOS 4.2 builds and the iOS 4.2.1 golden master seed is suggesting, however, that Apple will be offering a free MobileMe tier to users. The evidence comes in the form of a new private framework known as AppleAccounts.framework that includes a series of device-specific error messages referring to free MobileMe accounts. In particular, the error messages include alerts regarding having reached "the maximum number of free accounts" for a given device and certain devices not being "qualified for free MobileMe service".
MacRumors also found an error message that restricts certain Apple IDs from being used with MobileMe email.
"This Apple ID cannot be used for MobileMe Mail, but you can use it for other MobileMe services."
It's thought that Apple may be planning to use your Apple ID to offer over-the-air syncing. We'll keep you up to date with more information as it becomes available.