Calendars and Contacts Sync after iCloud transition
You're right, iCloud requires iOS 5 or later on iOS devices and OS X 10.7 (Lion) or later on Macs.

http://www.apple.com/icloud/setup/

http://www.apple.com/support/icloud/

I'm pretty sure you can still use cable sync to update the information on your older iOS devices so they can coexist when/if you migrate your Mobile me account to iCloud.