Here's a neat party trick for you.

I had a MacGyver moment in the past where I made a phone call with only are pair of old earbuds and a phone cord (no switches, no dial pad).

A speaker is basically the same thing as a microphone in reverse. Normally it takes an electrical signal to move a physical element that creates the sound waves. But you can also move the element and it will generate an electrical signal.

To dial you can use the old rotary trick. The old phones dialed by pulses of quickly disconnecting and reconnecting. You can do that by hand if you want but it might require a little bit of practice and dexterity. Basically if you want to dial a 5, just disconnect the wire from the headphone to the phone cord and then reconnect it 5 times in a row.

You have to both listen and speak through the ear bud. Not the best quality or easiest to do but it works.