I guess I should also add, based upon something I read recently, that "missus" is also an accepted spelling, as already suggested, i.e., "I do only what the missus tells me to do." I don't think that would be acceptable to use as an official title though. In that case, you'd still have to say "Mrs. Smith". I couldn't locate a reference for "Misses Smith" though I'm pretty sure I've seen that before. Maybe its been "Missus Smith" but I've never read that either. I'd probably stick with "Mrs. Smith".