I use 2 modems on the same phone line (ADSL ) BUT not both at the same time,
I have to unplug one of them from the Telco socket , to get a connection ,
why do I do this I have a second puter in another part of the house , as a backup to my main one, and it is also my puter workshop, it works for me if I need to transfer files , I just us my memory pen drive 1Gb