What is the word trick that uses words for every letter of another word?

I think what you mean is the NATO Phonetic Alphabet which replaces letters with Words used in certain radio and telephony transmissions to avoid misheard letters/Words (a=alpha b=bravo c=charlie d=delta etc, etc.)

More information about it here:

http://en.wikipedia.org/wiki/NATO_phonetic_alphabet

Hope I helped,

Joric.