The Phonetic Alphabet is an easy substitution cipher used by airplane pilots. The main reason for using it is that some letters sound really similar (like B, P, D and T), and can easily get confused over a bad connection, but the words that represent these letters sound quite different (Bravo, Papa, Delta, Tango) and can't be confused so easily.
Here is the alphabet:
Bravo Romeo India November Golf Mike Echo Tango Hotel Echo Papa Alpha Papa Echo Romeo
You can use the phonetic alphabet in memory games, or a general knowledge quiz, or break into teams and send phonetic alphabet messages by phone or by calling from one room to the next. You can even use it in a game like "battleships" where each player is only allowed to use the phonetic alphabet.