Like all gateways, there are pros and cons. For this device, one of the biggest cons is the firmware is custom and comes from Comcast who has a very poor track record with software. There are many missing features. However, the device itself and the firmware appear capable of this function, but the admin site presented to the user lacks any way to control this. You have several options:
If you need the router function and wish to keep the TG852G/CT, then call the gateway support folks at 800-363-2416 and have them disable the wireless radio and ONLY the radio. I understand its something they can do, but I have only heard that 2nd hand and it may just be some user's misinterpretation of bridge mode (which disables the entire router function including wireless). Call and ask if you're interested.
If you don't need the router function or have your own wireless router (which I highly recommed), then again call the support folks at 800-363-2416 and have them place the gateway into bridge mode which effectively turns the gateway into a cable modem with EMTA. The wireless and routing and admin site functions are completely disabled.
Replace the gateway with a regular cable modem and get your own router.
I personally recommend #3. However, #2 works well but is essentially the same as renting a regular cable modem/EMTA (for Xfinity Voice) from Comcast. If you buy your cable modem, you can get rid of the $7/mo rental charge.
After hours on tech support, they simply could not turn off the WiFi and/or put it in Bridge mode. Their management system would indicate that it was off and they hoped the power of words would convince me that this was the case despite staying connected to the WiFi the entire time and having access to the web management interface.
Fortunately, I had a friend that owned a DOCSIS 3.0 modem prior to getting the triple play and was able to swap that in. Boom magically better, my connection went from intermittent to rock solid and the speeds are faster than with the Arris unit. So I highly recommend Baric's option 3 as well.
The Motorolla Surfboard SB6120 and my fancy new ASUS RT-AC66U are working like champs.
Comcast should be ashamed they put such a shoddy piece of hardware out there. A non-technical layperson would probably get conned into paying for that sketchy support package.
Adding to this my support to provide your own device. I contacted comcat to shut off my wifi and they told me a tech would have to come out and do this... after calling BS, they then told me they can do phone support, for a $40 enrollment fee, and 15 support fee... just to shut off the radio on the wireless. They proceeded t tell me it wasnt an easy task... again i called BS.
I am a networking professional that specializes in routing/switches/wireless and related technologies and explained to them that this was an easy procedure. In short, they played a BS game and wanted to charge me rediculous fees to shut off the radio on my modem. For that price, i am just going to buy my own modem and not have to deal with their garbage. Comcast customer support stinks horribly, unfortunately/however, their service is the best in my area.