An email received by a Macrumors reader shows what happens when the iCloud space allotted to your iOS devices is used up. The email comes addressed from the ‘MobileMe Quota Service’ and specifies that your devices will no longer back up or save data to iCloud. It also lists the actions you can take once you’ve received the mail.
The interesting bit here is that iCloud storage is linked to your me.com email address as well. That means that if you use up your storage space with iPhone backups, you will stop receiving email to your me.com address. This seems like a poor way to handle email and having a shared storage space with backups, which can very quickly increase in size (my iPad backup is 3GB and I don’t even have all of my apps reinstalled after upgrading to iOS 5), seems like a quick way to annoy users of the new iCloud email service.
In order to resolve the situation, the email suggests that the user purchase more storage from iCloud. To do this you can visit the Settings>iCloud>Storage & Backup screen and tap on ‘Buy More Storage’. Currently nothing happens in iOS 5 when you do this.
It’s unclear at this point whether the email that you get sent will just disappear, get bounced back to the recipient or be held in a queue until you upgrade your storage or delete backups. Apple has yet to announce pricing on additional iCloud storage.