Would the PCI-E one work under Linux? I've got an old 98/XP/Linux machine that would be fun to stick a modem into for the novelty. Unfortunately the PCI slots are all taken up
The other interesting thing about Winmodems/softmodems, is that they could also be used for stuff besides serial data transmission. In particular, you could use them to send/receive faxes and handle voice calls. This latter ability was particularly neat.
No idea if they're still supported, but the Asterisk telephony package could even use inexpensive PCI modems as part of a PBX, to connect to analog devices on either the internal (wired phones) or external (POTS phone line) sides. This is a bit less impressive today, when you can buy a cheap SIP ATA for $20, than it was in the late 90s / early 00s when I first heard about it.
Why not use the USB one? https://www.usr.com/products/56k-dialup-modem/usr5637/