O vs. 0

I wish people would learn the difference between the letter "O" and the number "0". In all honesty, so many people are horrible at the English language, I choose to ignore most grammatical mistakes, but this is one that really bothers me to no end. When you give out your phone number, zip code, or even if you are counting, use the number and not the letter. Seriously, how hard is it to say zero instead of "oh". If I were to take it to heart and dial the letter "o" on the phone than that would be a 6 and not a zero.
I also strongly dislike it when verification codes has an "o" or a "0" in it. For example, when you need to type in an authentication online (and if you don't know what I mean, than forget it) Most sites will put a slash through the circle to indicate it is a zero, but if I use the wrong one and it locks me out, so help me, I will probably never go to your website again (i.e. trying to post on blogspot, send message through FB etc.)
So people, if you live in an area with a zero in the zip code, say zero and not oh. In my mind, you just look more stupid if you don't....
Now I know I am not perfect, but I strive to do as well as possible and try to learn from my mistakes.