The Quattro2-DTI (MT305) comes with a USB connections and a RJ type modular jack. The USB is designed for Voice or Video over IP (VoIP) or can be used for playback of your computers media player on a PC or MAC computer.The RJ connection allows you to connect to Digital, Analog, and Cellular phones. TheQuattro2-DTI is supplied with 4 cables:USB to USB - to connect with your computer. RJ male to RJ male – gray ; RJ male to RJ male – black; power supply - Bridging - The Quattro2-DTI will bridge the USB and RJ connections together for a three way call. An example would be if you were on a Software video call and you wanted to bring in a participant who might be at the airport and would like to contribute to the meeting. You would call him or her on the telephone that is connected to the Quttro2-DTI and it would bridge that person’s audio in to the video call. You could also make the call to a bridging service so multiple people would be connected to the video call.