I haven't been able to find a use for them myself. Our "land line" is now a MagicJack line fed by our cable internet service, so even as some kind of last ditch "underground railroad of DOS systems using dialup to communicate covertly", I have no way to actually dial out with them.

I will say, the suggestion to use a house's pre-installed phone wiring for modem based networking (obviously for vintage systems) is probably the closest thing I've seen to a legitimate use for dial up modems in 15 years. Still, I have no phone wiring in my office but I DO have ethernet run to three floors. Also, I'm pretty sure our phone wiring is shot since the house is almost 100 years old.

I have gotten rid of lots of them, but I do keep a box of them around just in case there is some odd IC or resistor that I need. Obviously the newer ones with few components are useless for this, and, admittedly, I have yet to find anything I needed on a modem. 😮

not sure what kind of ethernet speed you care about on all those floors but if you can deal with 100Mbps in one of them, you can run up to 2 phone lines on a CAT-5/6 cable. 100Mbps ethernet only needs 2 of the 4 pairs. Gigabit needs all 4.