Following the unveiling of Apple’s iCloud migration tool for developers, more details have emerged concerning what will be happening to MobileMe users and their subscriptions once they make the move.

As discovered by MacRumors, MobileMe subscribers moving to iCloud will be automatically signed up for the additional 20GB storage plan, that Apple offers to all iCloud customers for $40 a year. More precisely, migrating users will be given the same amount of storage they had paid for in MobileMe, without any additional charges until June 30, 2012.

There is a catch however. As a former MobileMe user, Apple signs you up for this recurring extended storage subscription automatically. If you decide to keep it, or forget to switch to the free 5GB plan by the end of June next year, you will be billed another $40 for the next year of storage.

Furthermore, it’s important to remember that Apple won’t be offering some of the MobileMe services in iCloud. For example, your photo and web storage will be discontinued come June 30. Until then however, you’ll still be able to access them, even after you move to iCloud. On the other hand, your preferences, widgets and keychains will be deleted from Apple’s servers the moment you migrate to iCloud, and you’ll have no way to access them after that. More details can be found on Apple’s website.

Any other tidbits we should know about? Tell us in the comments!