The speaker in an old telephone makes a great lo-fi mic. Just wire a 1/4 inch jack straight up to the speaker and enlarge the telephone jack hole to mount it. A small piece of towel helps to muffle some of the air noise.
First solder wires to the audio jack, then install in the newly enlarged hole. Cut the wires to be long enough so you can easily attach them to the speaker (next step) after the audio jack is installed. The audio jack won't fit through the body of the phone, so you need to install the jack before screwing the wires to the speaker.