The ID I want to register has been taken
This article provides suggestions if you would like to obtain a Yahoo! ID that is now unavailable.
Yahoo! is one of the most commonly used email and portal services on the Web. Because of this, many ID names are already taken.
If the ID you want is in use, you will be given the option to choose something different without re-entering the registration information. To create variations on an ID, you may choose numbers; add an underscore (_) or dot (.) character; or try creating the ID with the "rocketmail" or "ymail" domain.
Example: If the ID you are trying to create (such as "email@example.com") is not available, try the following variations:
In the event these options are not available, you may need to try a totally different name base for the account ID.