When I was in training for work at a call center, our instructor told us that no one would call us and wish that we had a great day, trying to give us a reality check as to the nature of most of the types of calls we would receive. Every once in a while, I like to call my customer service line up, and do exactly that. My challenge for you, is to do so, wish them a great day, and post the results here.
Isn't that what you normally do, though? Whenever (which isn't often ) I end a call with a callcenter/similar, I tell the person I've spoke to "Thanks, and have a good day!" (unless they've been useless, of course).