Did you check to see if an @icloud.com email address was already added to your iCloud ID? To check, you can go to https://appleid.apple.com, click on Manage your Apple ID, sign into your iCloud ID, click on Name, ID and Email Addresses on the left, then check the alternate email addresses listed to the right.
If the @icloud address is listed as an alternate address you can use it now; it will receive email in your existing iCloud inbox. This article explains how to make it your default on your phone: http://support.apple.com/kb/HT5441.
If it isn't listed, you would have to create a new account in order to get this, then migrate your iCloud data to the new account. If you want to do this, reply back and I'll give you the steps.