I've had this for 8 months now....
You only have to pay for the extra storage right?
With Windows Phone 7, you get 25GB of Skydrive for free, with calendar, mail, contacts and Office (Word, Excel, PowerPoint and OneNote) and the phone location/lock/wipe tools all for free. You don't even need a Windows Phone to use any of those services, just sign up, (even on a Mac).
Plus auto uploading of your pictures, and they won't delete them after 30 days. Any they have shown that with the Windows Phone Mango update you will be able to stream music from Skydrive.
Sounds like I've had iCloud for the past 8 months. Yes, I know there is more to it with APIs, but for what is offered in the base package, this solution already exists, just not on iPhone (yet).