Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 3_1_3 like Mac OS X; en-us) AppleWebKit/528.18 (KHTML, like Gecko) Version/4.0 Mobile/7E18 Safari/528.16)
I believe once you pick a name
for your @me.com you can't change it.
You can however change the email address for your apple ID if that's what you want to do?