Q: What do prisoners use to call each other?
A: Cell phones!

Explanation:  A cell phone is a celular phone, a mobil phone.  They are the ones that are replacing land lines as we stay connected 24/7.  Did you know that there are more than 6 billion cell phones in use?

Prisoners are kept in jail cells or prison cells.

This joke is funny because it uses the word “cell” in two different ways. Here is another way telephones are used: