just want to send a warn out there for people like I who be not tech savvy with modem - I find out the hard and long way that this modem will not work if you have Comcast internet and telephone . it only have a cable jack and a Ethernet jack -lrb- the Ethernet cable be the cable that run from you computer or router to the modem -rrb- . for Comcast voice , you need a telephony cable modem that have a cable jack , Ethernet jack , and a phone jack . I discover after a visit to fry that 99.9 % of the cable modem do not have phone jack - 3 of the 4 salespeople I speak with have never even hear of one have a phone jack . however , the best buy that have a Comcast installation center in they do sell the special telephony cable modem -lrb- brand be Arris -rrb- , but it cost $ 150 . I be sure I could have find one cheaper online , but I be pretty do with it by then . the rental fee for the Arris modem through Comcast be $ 7 a month . it would take over 21 month of rental fee to pay off the $ 150 price , and by then something new would be on the market . so I just bite the bullet and rent from Comcast . Hope this info save someone else a day of frustration .