I've seen people do it on a regular phone, like if the conversation was getting heated between two men. Because at that point, you dont need the speaker to your ear, you're not trying to hear anything the other person is saying. Anyone remember that Biggie video? I think it was called "Alarm", he's sitting at his desk talking to puff on the phone, about dudes trying to break in his house, he's talking into the receiver like that.