This is not correct at all. It’s Comcast’s policy to support any modem on the supported modem list. From first hand experience with half a dozen non-comcast modems, and way too many support calls and site visits to count, never once have they even suggested that I should use their modem, and they have never refused support or otherwise shown any resistance.

I’ve also never had a problem activating a modem. They ask for the MAC, model number, and sometimes S/N, then it works. The model and S/N are optional and don’t even have to be correct.

They’re a terrible company and I would not deal with them given the choice, but this isn’t one of the reasons why.