It amazes me how many seemingly educated people (politicians, newsreaders) prefer "an" over "a" when speaking a word that begins with "h".
You know the sort of thing: "This is an historic moment."
With a word like "historic" ("hotel" is another), pronouncing the "h" is optional. So, you can say "This is a historic moment", or "This is an `istoric moment". Both are correct -- anything else is just ignorant.