Yeah, that's definetly Mel. This was probably around the time of "Daffy Duck's Quackbusters" which would actually probably explain why they'd have spare Mel Blanc clips and spare "shilling out Bugs Bunny" animation cells lying about.
I didn't even have to watch the clip. I remember the event vividly, I recall being told ONCE about the rules of the 1-900 number. I never had to be told twice.