Two Can String Talk
Talking over two cans (or cups) and a string actually works. It is necessary to keep a tight string between the two ends, usually requiring a direct line. So long as the string is tightly secured, it will carry voice data.
Example setup: Prerequisites:
2 people 2 paper cups 1 long non-stretchable string (e.g. kitestring) 1 hole puncher (needle, awl, etc) tape or good knot tying skills Method: