My memory was that she had bad reception, but that the call wasn't cut, and when she hung up, she thought she had done a good job until corrected by Jerry. But I haven't seen this episode in over two decades probably, so my memory isn't going to be exactly right.

It was more that the person you were calling meant so little to you that you made the call while you were doing other things. Back then calling someone was almost like meeting them for coffee, often you would pre arrange the rough time you would call, and you were both engaged in the activity because you had to be at home sitting next to the phone. There was a certain effort to it that would seem lacking if you just could pull out a phone while you were walking down the street.