I saw similar product from another company but I bought this product because of the Andrew brand; plus this device is better looking than the other one =) When I got my unit, I connected my regular phone on line 1. Called up a friend of mine and after 12 minutes, I would hear annoying tones. We hang up and called again. After 3 minutes on the phone, the annoying tones were back. Hang up and called again and still got those annoying tones after 3 minutes. I contacted Amazon's customer service and requested a replacement unit. Amazon shipped the new unit express. I connected the new unit and it worked perfect. I made a 30min call and the sound is clear. No more annoying tones. It would be great if caller ID is passed by this device.I left one star because product documentation is poor. They could have done it better by using detailed drawings for the line connection.