Even a soft-modem needs hardware. For example, my new HP computer has a soft-modem and it works through a PCI card, and it is called a PCI soft-modem. Among other things, it has the RJ11 physical connection to the phone line. It is this PCI card that will have the REN and other FCC required info.
I imagine some motherboards could have this functionality so that a PCI card isn't needed, but whether it's a PCI card, or it's on the computer motherboard, it must contain all FCC Part 68 and Part 15 info, or it won't be in compliance with Federal Law.
If it will help, tomorrow I will pull the PCI card and see what info it provides.
What are you using for a terminal program?
Don