Who you gonna call?
I`m pretty sure everyone knows this catchphrase from a theme song from "Ghostbusters" movie. But I`m little confused about the grammar: I was thinking that way: "gonna" stands for "going to" (I`m going to call the ghostbusters) so to make a question I need to have something like "Who are you going to call?" but the catchphrase is different.

Please explain where I was wrong and what is the grammar behind the phrase.

Question

Who you gonna call?
I`m pretty sure everyone knows this catchphrase from a theme song from "Ghostbusters" movie. But I`m little confused about the grammar: I was thinking that way: "gonna" stands for "going to" (I`m going to call the ghostbusters) so to make a question I need to have something like "Who are you going to call?" but the catchphrase is different.

Please explain where I was wrong and what is the grammar behind the phrase.

Answer

You're not wrong in the slightest. In "street English", little auxiliary verbs are often the first to go ("Whaddup?" for "What's up" for "How are you?"). So take the perfectly grammatical sentence you started with:

Who are you going to call? => Who you going to call? => Who you gonna call?

Voilà, a catch phrase is born! :)

Answer

This expression was devised as a catchphrase for the film, and importantly it was chosen as the main lyric for the film's theme song. Don't look too hard for grammatical perfection in such things - rules are often broken and artistic license employed in such cases.

Answer

Yes you're correct. The grammatically correct phrase is "who are you going to call?", but the more slangy "who ya gonna call?" sounds more amusing :P

Answer

Suspect any sentence with "gonna" or "wanna" in it.