Can I Use 2 Modems

Our Internet and Voice service were split by during a service call quite a while ago using an ordinary coax cable splitter.  This provides redundancy with an old TG852G  just for Voice and a Motorola Surfboard 6580 for higher speed Blast internet and home network management.  Even if one service goes out, we still have a fallback.  And it's happened often enough to be tested here.   Unless a storm drops telephone poles and cell towers all over.  Like Isaisis. 

The Arris CM1150V looks like a good current one-box solution, but it is pricey.

I just recently tried this, but there's issues with Comcast configuring my modem.

From the logs on the TM822G I was using for voice, it fails when the system tries to configure it.

However, Comcast isn't accepting the issue is on their end at face value (despite the logs indicating the issue).

Since they are in control of the fiirmware updates for the devices, I can't even update it myself.

Good luck and try to get a good technician.

Thanks to those who replied to my initial post.  Since then I did an online live chat with Comcast tech support who said I can’t use more than one modem.  I then talked in person to a Comcast field tech and by phone to Comcast tech support. 

The field tech said he hadn’t configured separate telephony and cable modems for customers but that Comcast techs do it all the time for themselves, with what he called a modem exception in the Comcast system, and separate config files on the two modems so one is configured only for phone and the other is configured only for Internet, and a splitter on the line. 

I then reached Comcast tech support by phone after discovering that I first had to go through the IVR system and allow them to reset my modem even though I didn’t need it, and then tell them that didn’t solve my problem.  I then got right through by phone, and the rep told me right away that 2 modems are no problem, I just call them when I have my new non-telephony cable modem.  They then configure my account for two modems, one for phone (the old modem), the other for Internet, and I schedule a $40 service call for a tech to do the physical setup.  It’s a bit disturbing to hear that Comcast couldn’t configure bolohead’s TM822G modem (the same model I have) for phone only.  Bolohead should escalate to Level 2 or even Level 3 tech support if necessary if not already done.  My experience with Comcast tech support over the last couple of years has been very good unlike the bad old days. 

I plan to try this myself and will report whether successful. 

Thanks to durgin99 for suggesting the CM1150V (which I think is a Netgear product, not Arris) as a good one box solution (telephony and Internet), but it is pricey at $250 and would defeat the whole purpose of using an existing old but perfectly functional telephony modem for phone only and a good new Internet only DOCSIS 3.1 cable modem such as the Motorola MB8600 ($160) or Arris SB8200 ($149), neither with the defective Intel Puma chipset.

Please update the thread when you are able (or unable) to get your setup working.

Currently, I'm still waiting for a tech call, since my TM822G is failing to be provisioned for voice still.

Report on Installing 2 Modems, 1 for Voice (telephony), 1 for Internet: Success.  Briefly: This morning Comcast field technician came ($40 service call) and:

• checked Comcast signal at the street, at the incoming point in my basement (where there’s a Comcast amplifying multi-line device since this house was originally wired for about half a dozen cable TV jacks), and at the phone/Internet jack in my home office [perhaps an inadequate signal for various reasons would cause a cable modem not to function or provision correctly],
• installed a splitter on the coax cable from my wall jack providing phone and Internet service,
• connected 1 cable from the splitter to my old Arris Touchstone TM822G telephony cable modem,
• connected another cable from the splitter to my new Motorola MB8600 non-telephony cable modem,
• called his Comcast tech support office, made sure my new modem had been added to my account (which I had done by phone with tech support a few days before, though it was not then connected yet), and had them create and activate new “boot files,” one for the old modem enabling only phone service and disabling Internet service, the other for the new modem configuring only Internet service, and restarted the modems,
• moved the Ethernet cable coming from my router from the old cable modem to the new cable modem.  

I then tested both my phone (got a dial tone) and my Internet and Wi-Fi service (it worked).  

I learned that “boot files” are configuration files that the Comcast system pushes to customers’ cable modems when they connect to the Comcast system and control whether the modem functions (or tries to function) as a telephony only modem or an Internet only modem or both.  

Additional details:

• The tech said the TM822G is the oldest version of that model cable modem still listed as a Comcast-approved modem and supported by Comcast, and that previous versions are considered at end-of-life and may not be able to be provisioned.  But the TM822G should have no problem.  The cable modem is a simple device that either works or doesn’t work, and if it works, it should be able to be provisioned by Comcast with a boot file that makes it work for phone service but not for Internet service.  
• Regarding firmware, I previously talked to Arris tech support, who advised positively that there have not been any firmware upgrades for this cable modem.  This is confirmed on the Arris website which for this model modem states that no firmware upgrades are available.  
• The Comcast tech said that for all cable modems, whether rented from Comcast or owned by the customer, any firmware upgrades that the manufacturer issues go to Comcast and the other Internet providers who then push the upgrades to the cable modems of all customers who have the particular model.  Some brands and models of cable modems enable login by the customer and manual installation of firmware upgrades, but the TM822G does not have that capability.
• You can access the GUI interface on the TM822G by typing the IP address 192.168.100.1 (or http://192.168.100.0).  That takes you to screens displaying various status info, system information and hardware and firmware versions, and recent event logs.  It does not allow for installation of firmware upgrades (if there were any). 
• My TM822G GUI interface display included the following:

“Firmware Name:  TS0901103M2AS_112019_MODEL_7_8_PC20CT”

“Firmware Build Time: Wed Nov 20 14:16:51 EST2019”

Copyright notice: “ARRIS Enterprises, Inc. 2019 All rights reserved”

• The inclusion of “2019” on all three lines of the above firmware information is puzzling, given that I bought this modem in 2015 and have never been aware of any firmware upgrade, and both Arris and Comcast have said there are no firmware upgrades for this modem.  I surmise that either the techs and the Arris website are wrong about the absence of firmware upgrades (not likely), or the modem’s GUI interface firmware information represents not what we may think of as firmware upgrades but rather the date of the latest boot file pushed by Comcast to the modem after being made available by Arris to Comcast, perhaps stored on an eprom and regarded by the Arris software as firmware.  
• I cannot confirm whether that’s true by looking at the GUI interface on my TM822G again now after it has been given a new boot file to see if it shows a current date.  Since that modem is no longer configured for Internet, it’s no longer part of my home network and I can no longer access its GUI interface via IP address.  Maybe Comcast tech support could, but I didn’t think to ask.  
• Regardless of all that, the bottom line is that if a TM822G is functioning as a telephony modem for voice and Internet service, it definitely should be able to be reconfigured by Comcast with a revised boot file, as mine was, to function only for voice, allowing installation and configuration of a new non-telephony modem for Internet only.  If the modem is not currently functioning, then perhaps there’s been a hardware failure.  

If I can be of further help, please advise.