said by Bob4:TV does not use a modem.
Phone service requires an OOL account on the same modem.
What you want to do requires two OOL accounts.
Seems silly to do, when all you need to do is run an Ethernet cable somewhere.
I may be wrong but I think you are allowed to have a Phone-Only modem (ie: They do not provision an Internet address to it) without incurring a 2nd Modem Charge. This impression is based on a memory that Ultra was/is? not compatible with Phone Support so a 2nd modem was supplied for the phone support.