Question about modems

[Fred Cisin]

On Wed, 13 Nov 2019, Electronics Plus via cctalk wrote:
> And here my problem is that I have the old modems, but I can't test them 
> because I no longer have a land line. Is there any way to test an 
> internal or external modem without anything except broadband or cellular 
> connections? I know I can't test the acoustic modems, but I was hoping 
> to be able to test internal ISA and PCI, as well as external modems from 
> 300 baud to 56k. Perhaps there is some inexpensive gizmo available?

A "telephone line simulator".
In some cases, you might be able to just connect them, with a power 
supply.
One set to "Originate" and one to "Answer", of course.
But, you also want a "dial tone".
And, if you want to test answering capabilities, then you also need a 
"ring simulator", which is 90VAC at 20Hz.  (often a lot of tolerance)


What do you need to do to use an acoustic modem with a cellphone?
You can get a "retro" handset for a cellphone, that will fit the rubber 
cups, but, will it work?