Not sure if this applies to all markets, but found this info for atleast some areas:
"Vacation Rate" option for cable service If you subscribe to cable television, you can take advantage of the "vacation rate" option. Your account must be current and you must plan on vacating your primary residence for a minimum of 2 months and a maximum of 6 months within a 12 month period. The 12 month period is from when you first start the seasonal program, not from the end date of the program. Your service remains active at the tap or utility pole at your primary residence during your absence, and Comcast equipment must remain in your home. Your service is restarted with one telephone call. The monthly fee for video and high-speed internet access is $10.00 per month for each service.For more information, call Comcast customer service.