Absolutely. My Mum's typewriter had numbers running from 2 till 9, I think. I used a lower case ell for one, and I guess capital oh worked for zero.

Which reminds me of a textbook on BASIC where the authors insisted that capital oh was always shown with a slash through it, to differentiate it from zero, which was always displayed without a slash. This is backwards to many implementations, since null and zero are similar concepts.

Of course, if you're Scandinavian, and you already have the letter oh with a slash through it. It's always something.