Its true. You need Yahoo PLUS even for Yahoo messenger.
They are integrated in yahoo server system and if you like it or not need subscription to yahoo PLUS.

Its simple you use the same mail and user name for messenger yahoo like your email.

Hey boys and girls who use yahoo...I really don't understand what its problem to pay yearly so cheap subscription to Yahoo Plus few rials...?
Calculate how much you pay for using browser and Qhell every month and trust me in 2 months you pay yearly Y.Plus.
And you can use Yahoo mail in POP Outlook whats come very useful. At least for me.

Hope this help you.