I had the exact same problem so I figured I should be nice and share what I had to do to fix this...
Delete the icloud account from your 900. add a new account but this time select advanced add (best I can tell the 900 is getting messed up between me.com vs icloud.com).
1. Enter your (address)@me.com account and password
2. For the incoming server put the imap settings for icloud imap.mail.me.com:993 (check that with a google search I don't remember it exact but I think that's right)
3. Outgoing server is SMTP.mail.me.com
4. Check all the boxes for requires auth and SSL
5. Let it sync and enjoy.
I was somewhat pissed that it wasn't working until I fixed it with these steps. 5 days later and still good, keeping my fingers crossed, now if only it would sync pics and calendar I would be in heaven but u take what u can get on a windows phone (work made me get it, I miss my iPhone)
Good luck,
Badatthis