Ok, so far so good.
I've sent an email to possible yahoo ID combinations and I got the below reply:
(first - my first name, last - my last name)
Message from yahoo.com. Unable to deliver message to the following address(es).
<[email protected]>: This user doesn't have a yahoo.com account ([email protected]) [0]
<[email protected]>: Sorry your message to [email protected] cannot be delivered. This account has been disabled or discontinued [#103].
<[email protected]>: Sorry your message to [email protected] cannot be delivered. This account has been disabled or discontinued [#102].
<[email protected]>: Sorry your message to [email protected] cannot be delivered. This account has been disabled or discontinued [#102].
I felt lucky today. Went straight to yahoo sign-up to get my yahoo ID containing my name. Surprise: This ID is not available.
So...what?