Messenger Plus! 4 (Messenger Plus! Live) never had this feature. This feature was removed somewhere in the past, not sure if it was somewhere during 2.x or 3.x, but it was indeed removed on purpose like MattyRid said, and it won't come back.
Messenger Plus uses the sponsor to generate some money from freeware software, Microsoft does exactly the same with their banner on the contact list. It just wouldn't be fair if Plus! removed Microsoft's banner while installing the sponsor. And yes, Microsoft could probably do some very annoying things if Plus! starts to piss them off
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