Following the path that has been set to free up inactive username account names (for at least 12 months), Yahoo offers the chance to acquire an email account with the username you always wanted to have.
Yahoo wish list is open for you, so that you can add there your desired usernames in all of Yaho0’s services like Yahoo Mail, Flickr and others. The only thing you have to do is add in order of preference your desired usernames and wait until the 7th of August, to see if you won! In case you made it, Yahoo Mail will inform you mentioning that your desired username is finally yours! If you request an availalbe username you will be notified at the same time that you’re ready to use your account.
You can get access to Yahoo’s wish list, here.