Let me say first that I generally like Comcast products, and I have been a subscriber to Digital TV, Hi Speed Internet, and Telephone service for over 4 years. What I do not like are the shoddy business practices. This includes the practice of renting digital converter boxes and cable modems. The first two digital converter boxes are free, which is reasonable, but then you must rent a box from Comcast for any additional TV's that may be in your house.
I finally got tired of paying the $7 monthly rental fee for an old Motorola SBV5220 cable modem (EMTA type, which includes telephone), so I purchased an identical modem from a seller on Amazon.com for about $21 with shipping. Unfortunately the seller shipped a model SBV5222. I tried to connect it to the cable, but was unable to access the internet, and the phone would not work either. I reconnected my rental modem and called Comcast on December 26, 2011. The service tech was very helpful and took all the information he needed to connect the modem, including model, serial number, and MAC addresses. He claimed he had entered all the information into the "system", and all I needed to do was turn in my rental modem and Comcast would start my service. I drove the 10 miles to the Comcast office and turned in my rental modem. Then I drove back home, connected the SBV5222 modem, and called on my mobile phone, connecting with another service tech. This tech claimed there was nothing in the "system" regarding my new modem and he spent about an hour trying to enter the information. He finally claimed he could not get the modem "provisioned" which is required for it to work. In all fairness, the SBV5222 is not on the Comcast Approved Modem list, while the SBV5220 modem was, although considered EOL (end of life). Which tech was telling me the truth, I do not know, but it appears someone was incorrect.
I then drove the 10 miles to the Comcast office to get my old modem back, but instead they would only give me a new Arris TM602G EMTA modem, which I took home and connected. Another half-hour cell phone call and I was back with a working internet and telephone. I contacted the Amazon seller, who refunded my total price including shipping and told me I could keep or sell or whatever I wanted to do with the incorrect modem, since return shipping would be more than the value of the modem.
Next I ordered another SBV5220 from a seller on E-Bay, again for about $21 with shipping. This modem arrived on January 10, and was indeed the correct model. On January 11, I connected this modem and opened Internet Explorer, to find a Comcast web page where I entered my account number and phone number, and in a few minutes I had internet access, but no telephone. I then opened a live chat session with a Comcast service tech, who claimed the only cable modem I could use was an Arris TM702G which oddly enough was available at the Comcast store inside Best Buy for only $170, except they were out of stock when I checked a week previously. I explained that that was just not true since I had been using an SBV5220 for over 4 years, and had been using a TM602G for the last week. He claimed I had to have the latest DOCSIS 3.0 model, although both the modems I had been using were DOCSIS 2.0 models. After about 30 minutes I asked for a supervisor, and another person came online, claiming to be a supervisor. He took all the information and claimed the SBV5220 would not work, and that it was not on the approved list. I gave him the internet site for the list, and explained if he clicked the EOL box he would find it on line 107. He continued for about an hour, and finally took the MAC address and serial number. Finally he claimed the only modem I could use was the TM722G from Best Buy.
I next re-connected my rental modem and called the direct phone line to have a modem provisioned (800-931-0790) and talked to yet another service tech. I gave him the model, MAC address, and my account information. He offered to call me in a few minutes when I had my SBV5220 modem connected, and within 5 minutes he had it working with the telephone.
I returned the rental modem to the local office, and was told by the lady at the counter that the modem I purchased was probably stolen from Comcast and I would likely be charged a rental fee in the future, although I explained to her that if that happened Comcast would not receive another dollar from me and I would cancel my phone, internet, and cable TV and get service elsewhere.
I have never had so many people lie to me and stall just to collect a measly $7 additional fee when I am paying over $110 a month for their service! The practice of trying to force customers to pay a rental fee or only purchase the product from Comcast is extortion in its worst form in my opinion.