A question that I get asked all the time is why I pronunce the word "og-um."
The name of the early Irish alphabet can be properly spelled two ways.
The more commonly seen modern spelling is ogham, pronounced "oh-am." The Old Irish spelling, ogam, is pronounced "og-um." Both are correct. You can use either or both. I prefer the "ogam" version, but that's purely a personal preference. It doesn't reflect on a person's knowledge of the system at all (unless they try to tell you you're wrong when you use one of those spellings or pronunciations).