A woman is in bed with her lover, who also happens to be her husband's best friend.  They make love for hours and, afterwards, while they're just lying there, the phone rings.  Since it is the woman's house, she picks up the receiver.  The best friend listens, only hearing her side of the conversation:
"Hello?  Oh, hi....  I'm so glad that you called....  Really?  That's wonderful.... Well, I'm happy to hear you're having such a great time....  Oh, that sounds terrific....  Thanks.  Okay.  Bye bye."
    She hangs up the telephone and her lover asks, "Who was that?"