I'll be frank...I don't know a thing about this unit. I have used it before, and it works fine. It sounds similar to a bell phone. You can plug it into the jack and run it by itself or you can plug your phone into it and then only the external ringer will go off when you get a call. I'm selling it on here because I need to purge my phone collection. Thank you for looking, please feel free to ask me any questions you may have!