Firstly, just stop using the word 'Oh' in a telephone number. It's ZERO ‼
Secondly, let's all agree to use different symbols for zero and the letter 'O'.
Computer programmers have been doing this for ages (because they are different keys on a keyboard).
Computer programmers use the following symbol for zero. You should too!
I used an image for the above symbol since most fonts use a symbol for the digit zero that's nearly identical to the symbol for the letter 'O'.
So we'll need all font designers to change their fonts to use the above symbol for zero.
Talking of font designers ... stop using virtually identical symbols for the digit one and the lower-case letter 'L'. It's stupid!
Finally, we'll need every new keyboard to show this symbol on the zero key. Simples!
P.S. Sorry James Bond, but you'll need to become double-zero seven!