It's in 'The Pitch', just when George brings Susan into jerry's apt for the first time (right before Kramer vomits non her).
It goes kinda like this (might be missing a few things):
Voice: Are you interested in a subscription to TMI service?
Jerry: Gee, I can't talk right now... why don't you give me your home phone number and I'll call you back?
Voice: I can't really do that.
Jerry: Oh, I guess you don't want people calling you at home.
Jerry: Well, now you know how I feel.