Words that don't exist but should

I want there to be a gender-neutral title. I know about the pronouns in writing, I want one for speech. I want an alternative to Sir/Ma'am so that if I'm not sure about the gender of the person I'm addressing (or if they're outside the gender binary) I have something to call them. Actually, I would use it all the time. Also the same thing for Mister/Miss/Ms. So that when I'm writing a letter or leaving a voicemail, I have a title to use. I know that in that case, the standard advice is to write "Dear FirstName LastName" but sometimes I'm not sure how to pronounce a first name. What I would do in that case normally is say "this message is for Mr. Smith" but if the name is ambiguous (and even when it's not obviously so- remember that Leslie and Ashley are boys' names too. As, actually, is Evelyn) then I don't know if it should be Mister or Ms.

Why was English not designed for the problems of 21st Century life?