“YES you can buy your own box... BUT [Comcast will] tell you no that it is illegal and that you must disconnect it from their line.” Tom's Guide Forum · 13 years ago

Xfinity has transitioned to an all-digital platform and now recommends upgrading to X1 TV Boxes or using the Xumo wireless box for additional outlets.

If you are looking to avoid equipment fees or connect an older TV, consider these options:

Digital Transport Adapters (DTAs) are designed only for standard channels and do not support premium content, On Demand, or DVR features. Community Feedback

Users on community forums often warn that while the hardware is physically available, it is frequently a "paperweight" without official service authorization.

While buying a TV adapter is difficult, you can buy your own compatible cable modem to save on monthly rental fees. What's the difference between a TV Box and a TV Adapter?

“the product is 100% useless. Product cannot be used by Comcast/xfinity customers because the company has the power to activate the unit at which time they will bill the user a rental fee.” eBay Available Alternatives