This article outlines the most common issues around selecting a Twitter username:
If you try to select a username and see that it has already been claimed, you will need to select a different one. Remember the following:
Here are the possible reasons why you would be unable to claim a username that seems available:
If you try view a suspended user’s profile by navigating to their profile (by typing twitter.com/[their username] into your browser's URL bar), you’ll see the following message:
Trying to navigate to a deactivated user’s profile will return a message like this:
While we work to make more usernames available, hang in there and try to think of other ways to express your Twitter identity! Remember, you can change your username at any time.