zero and letter O

O123456789..........

why do people use o as a number.. i thought o is the fifteenth letter of the english alphabet and not a number...
well, zero is considered as a number but not o....

just thought about this when a very close friend slash classmate of mine Jomvi gave his celphone number to another classmate... so he said zero nine o six blah blah blah...

after that, i reacted "hei, o isnt even a number"... lol ( dont worry he is used to that.. he reacts more than i do.. lol)
so he reasoned out.. his point was that people are fond of using short cuts and short terms... waaaaahhhhhh

yeah right Jomvi.. lol