I made a can telephone once, following directions in a Donald Duck comic that was free with a pair of shoes. Both ends are cut off, and one end has a membrane made of grocery sack paper, greased, with a hole in it and a button attached to the string (repeat for other end). The membrane approach is way better than just using a can with the top cut off. Which is itself better, of course, than using a can with the top still on.
