Preview at WWDC likely in June, followed by September launch.
MobileMe to iCloud Transition Gives You 25GB Storage Until June 30th, 2012
While MobileMe and iCloud accounts are quite different there are some overlapping parts. iCloud will continue to house Mail, Contacts, Calendar, Bookmarks, Find My Phone, and Back to My Mac, while dropping support for iWeb Publishing, Gallery and iDisk. Meanwhile, iCloud adds iTunes in the Cloud, Photo Stream, Documents in the Cloud, Automatic downloads of apps and books, and iOS device backup and restore.
During the transition, Apple has promised to keep existing MobileMe accounts active until June 30, 2012. What wasn't entirely clear was how the storage requirements would shift over to iCloud. Current individual MobileMe customers have 20GB of storage included in their yearly plan.
Apple has decided to move this one-to-one over to iCloud and is automatically signing up MobileMe users to the 20GB (+ 5GB free) tier plan in iCloud at no charge. We previously detailed the iCloud additional storage pricing which puts 25GB of storage at a normal yearly price of $40 USD per year.
Users are automatically signed up for recurring billing with the next payment date for the plan to be June 30th, 2012 -- the same date that the rest of MobileMe shuts down. You may choose to downgrade before that time, and not get charged.
It's not clear how much an average user will need on iCloud. Apple claims 5GB "goes a long way". With the loss of MobileMe's iDisk, individual storage requirements could easily go down with iCloud, but the addition of iOS backups could easily push you over the free 5GB limits. Apple is expected to launch iCloud in the fall alongside iOS 5.