Imagine you are in the army. (I know its difficult -
I couldn't even do that 14 months ago) Imagine your
unit is somewhere in
the field. It is a real world
combat situation. You need
beans 'n bullets, as they say. You get on the
radio to your supervisor and tell him your
grid coordinates - a combination of otherwise
nonsensical letters and
numbers.
Or imagine this. You are working behind the lines a little bit. Your life is in no immediate danger. But your job is to pass information on enemies' locations over the radio. What if you get it wrong?
In either case the lives and welfare of many men are dependant on your ability to correctly communicate that information to the guy on the other end. Radio static, speech impediments or accents, and hearing problems are only a few possible interfering factors. You want to be absolutlely sure you are heard correctly.
Enter the phonetic alphabet:
Alpha
Bravo
Charlie
Delta
Echo
Foxtrot
Golf
Hotel
India
Juliet
Kilo
Lima
Mike
November
Oscar
Papa
Quebec
Romeo
Sierra
Tango
Uniform
Victor
Whiskey
X-Ray
Yankee
Zulu
And as far as numbers go:
1 - one
2 - two
3 - tree
4 - foe-er (two syllables)
5 - fife
6 - six
7 - seven
8 - eight
9 - niner
0 - zero
For maximum clarity and uniformity, each digit is said as if it were a single entity - for example: "fife tree two", not "fife thirty-two" or any variant.
With this system the difference between D and E (for example) is so great that it cuts through so much interference that with that amount you wouldn't be able to communicate anyways. There are no longer 9 letters that end in 'ee'. The syllabic pattern and wide variety of sounds in this system give each character a very useful uniqueness.
Aka the phonetic alphabet or military phonetic alphabet. Appropriate uses are during radio or other voice communications, or anytime you want to be perfectly understood - even in person. But its not like we all go around spelling eveything this way.