To do this you will need two mobile phones -they do not have to be on the same network but you will need to know the number of one of them. The only other items you will need are:
1. An egg cup, (make sure that the egg cup is made of an insulating material such as China, wood or glass – plastic will do. DO NOT use stainless steel or other metal).
2. A radio, AM or FM – you can also use your hifi.
3. A table or other flat surface on which to place the phones and egg cup. You can place the radio anywhere in the room but you might as well put it on the table.
Thanks to Val Stevenson!