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In spite of the Cable Act of 1992, other FCC, state/local regulations, many of us are still at the mercy of Cox and its monopoly like tactics.
Case in point is Cox's so-called "approved" list of cable, phones enclosed herein: https://www.cox.com/residential/support/cox-certified-cable-modems.html
While many might think they actually have an option to purchase one of the above, reality is Cox has you boxed in and I'll use my personal case as an example.
I'm currently renting the Arris TG1682 from Cox for approx $20/month -- quite a rip off on Cox's part as they buy these in bulk for approx $55/each so in a little over two months Cox has their money back and gouges customers for months thereafter on rental fees. The 1682 has 24 downstream channels, 8 upstream channels, incorporates (eMTA) phone telephony (voice over IP) and has a highly marginal WIFI built in capacity (their "Panoromic" WIFI) that, at best, underwhelms and is close to worst of breed.
I'd like to return this BOAT ANCHOR to Cox and purchase my own Arris / Touchstone TM3402 (32x8, DOCSIS 3.1) that uses CommScope's comm/voice stack (I believe much of this software is open source), has a superior processor, VoIP RJ11 jacks (for my existing Cox Voice Service), and (4) Ethernet RJ45 connectors, BUT Cox has the manufacturer in an exclusive / lock in and you can't find the TM3402 or equivalents anywhere -- in violation of so-called consumer protection regs/laws that provide us (in theory) the option to use our own equipment to avoid Cox's continued GOUGE on equipment rentals.
I'm close to Cutting Cox's Cord, dumping Cox Voice and moving to a better WIFI router (many already outperform "Panoromic") --- there are plenty of streaming services that flat out beat Cox's Monopoly pricing. Cox's software is slow and poorly designed - their streaming option on Windows is a total mess (kludgy, unstable), their remote/networking/app/menu software is slow and generally speaking (I'm a software designer) I'd give their overall software design/implementation across the board a rock sold D+ score -- very frustrating for many of us as we're paying for filet mignon and getting "served" Cox low grade hamburger with loads of "Hamburger Helper".
Cox needs to change their slogan - brand to : YOU CAN FIND BETTER, BUT YOU WON'T PAY MORE
Cox only has you "boxed in" for all-in-one devices.
Only Cox can issue an eMTA for their network. If you want an all-in-one device (DOCSIS, eMTA, WiFi), you'll need to rent from Cox. As far as DOCSIS and WiFi, you can buy whatever you want as long as the DOCSIS is certified.
Buy what certified equipment you want, connect it and exchange the 1682 for a standalone eMTA. Cox probably won't have a standalone eMTA, so they'll probably loan you another DOCSIS.
I would suggest the Arris TM3402 with your own stand alone router. That will get you DOCSIS 3.1 data and phone.