I like to listen to people having sex over the phone

It's a long story as to how I discovered that this turned me on, I'll make it as brief as possible: Basically I was talking to a girl I met on one of those chat line things, never met her in person before. She was hanging out with her male roomie while on the phone with me, and they started watching porn. She was commenting on how stupid the scenes and the music were to me, and I could hear them both laughing about it (you know how porn can be). Well, somehow I got turned on, and asked her if she'd let him eat her pussy while they watched it. She put me on hold, came back and said "He's down with it. We're gonna have sex though". So they had sex while I was on the phone, and she was describing it to me while it was happening... even for me to just ask her "what are you doing" and hear her say "having sex", and be able to HEAR it in her voice that yes, she has a c*ck in her that very second.... wow.... turned me on like CRAZY. Since then I've been able to get several girls to do it for me, including my ex-gf while we were in our long-distance relationship. So.... is this just kind of a combination of voyeurism and swinging, or what? Also, where do you think I could find girls who would be into this so I could have someone new do it for me? Pretty much every girl I've told about this thinks its hot, though they wouldnt necessarily do it themselves..... thoughts?