Two modems

I haven't personally, but I've seen many posts here over the years indicating that it's allowed. However, it may be a policy of theirs that varies between different market areas / franchises. It's best to confirm with them for your particular area.

Hello, @jjw1988 I have seen this setup on a few accounts. To use Xfinity Voice service, you only need one third party compatible embedded Multimedia Terminal Adapter (eMTA) or a digital Voice modem. You can rent an eMTA from Comcast. The best place to shop is our device info page which can help you select compatible 3rd party equipment. 

For more details see:

• https://www.xfinity.com/support/articles/requirements-for-equipment-used-with-phone
• https://www.xfinity.com/support/articles/requirements-for-digital-voice-modems

I have a separate voice modem at my house because of where the wiring is in my home for the phone jacks. You can rent the equipment from Xfinity.