That’s what I have in my car. Works great.
Looks like what I used to use to plug a Discman into a cassette. Didn’t figure I could do the same with a phone, not that I want to, but cool.
[off topic, but I can’t resist…]
brilliant sig!
[/sorry, mods. I’ll be a good boy from now on, I promise]
You can plug anything that takes a standard 3.5mm audio jack into it. Basically, any device that takes a standard set of headphones.
One interesting gadget I had back during the CB radio craze of the 70s was an 8-track adapter that worked exactly like the cassette adapters. It was an 8-track tape shell with a cord coming out of it with a 3.5 mm headphone plug on the end. You put the adapter into your 8-track slot. I plugged it into the line out of my CB radio and I could listen to it through the stereo speakers hooked up to the 8-track. It sounded good, much louder and clearer than the tinny sound out of most portable CB radios. Of course, nowadays the 8-track is deader than the dodo, so there wouldn’t be a market for one of these anymore.
I, too, once owned a blank cassette 
So I think that sounds interesting, and I google Prison Cassette Tape, and – who knew! “Prison Cassette Tape” is a standard catalog item.
Didn’t the RIAA wage a semi-successful war against the format? T
Some of them will play just fine even after decades but it is a crap shoot and the quality is universally bad because it was always an inferior format. It sounds like you aren’t talking about the cassettes themselves but the content. I can understand that sentiment just fine but you probably should transfer the ones that you value to digital media before the tapes degrade even more. Digital is forever as long as back it up but individual cassettes are analog and can go at any time. There is nothing worse than trying to fix a huge string of irreplaceable cassette tape with a tiny screwdriver, scissors and some Scotch tape. It usually works to some degree but the problem can be avoided completely just by transferring it to modern media.
You don’t even need a specialized service to do that. All it takes is a cassette player with an audio out jack, a computer with an audio-in and free software like Audacity that can even make it sound better than the cassette if you want it to. Just play it on one side, re-record it on the other in digital format and save the tape for posterity. You have the content in digital format and can do anything you want with it.
Now you can play your “cassettes” on anything from your TV to your Smart Phone or even share them around the world.