Quote Originally Posted by Quin 'n' Tonic
Maybe the ones you know. I know intelligent people, though. Stop generalising everything.
You're basing who's intelligent on who does or doesn't say "an" in place of "a" an you don't think that's a
generalisation?!

Apostrophes are used to indicate a missing letter so, yes, it is correct to use an apostrophe.
No, it's not. An is not missing a letter. An is a word in it's own right. Argue it with the dictionary:an - definition of an by the Free Online Dictionary, Thesaurus and Encyclopedia.