i totally understand your frustration, and i agree with a PP who suggested pulling some people aside in private and really spelling it out for them. Also, i like the idea of just hanging up on her when she calls and asks for the wrong person.
my full name is Kaitlyn, but i've gone by Kait for the majority of my life. (my mom & stepdad are the only ones who really call me by my full name - my mom gave me the name 'cause she liked it so much, so she's going to use it, gosh darnit!

) i
hate when people try to call me Katie - that's not my name, and i won't answer to it. i know that sounds like i'm being nit-picky, but when there are so many Kate/Katie/Kathryn/Kaitlyn's in my age group, you kind of have to stick with one and go with it. For instance, one of my best friends is named Kayti - if you don't speak the right name, you won't get the attention of the right person!
also...totally annoying when people don't spell my name right when i know they should have it down by now. Especially when it's on Facebook or in an email or something - like, really? It's RIGHT THERE.