EMTA compatibility

We've seen them allow this arrangement here many times before. You need to contact customer service and let them know what you are trying to do. Ask them to provision the new modem for data service and to provision the eMTA for voice service only. Good luck !

@robmidi 

If you have trouble finding a rep that knows how to set it up, please post back here and I'll escalate this to a corporate expert / specialist.

Your question is not completely clear. Do you mean will it also work for data or do you mean will it work for phone service only alongside your data only modem ?

Phone service only.  The DMARC is 60 feet from the office, where the EMTA is located, so the data modem (DOCSIS 3.1) is at the DMARC and the EMTA is in a cabinet in the office, connected to coax.  it has 4-RJ45 connectors on it, but are not used--only the phone jacks.  If the voice only would work, I wouldn't have to go to the Xfinity store to exchange voice modems.  Plus, the one I have has a 10 hour backup battery in it and the new ones listed on their site don't.  Thanks for your help!

I had almost the same setup, Docsis 3 modem, Docsis 2 voice for the past 8 years, worked fine until I upgraded plan speeds ( 400 to 800 ) this summer, it seems no-one could figure out what billing codes to enter to redo this combo anymore, so it wont work, If you get someone to setup both, the automated billing system will disconnect the data modem in favor of the voice, at least that what I went through multiple times this summer. Landed up purchasing a new 3.1 modem with voice.