Someone/Somebody wants to talk to you.
Now, if you'd like to refer to someone/somebody, then you normally use the subject form they, the object form them, or the possessive determiner their:
A: Mrs Patterson, someone wants to talk to you.
B: Did they not tell you what they want to talk about?
B: Alright then. Bring them in. We don't want to waste their time, do you?