Think

It depends on the context of the sentence, but it could be correct.
-Corey Johnson

http://johnsoneslinstitute.weebly.com/about-us.html

It's grammatically correct but it might be taken as a bit rude. In effect you are saying that making the call is not very important to you. If that's your intent then it's fine otherwise you might want to try rephrasing it so it's more polite. Here are some examples:
I'll call you back as soon as possible.
I'll call you back as soon as I have some time to talk.
I'll call you back as so

PreciousJonesIs this sentence correct?

Grammatically, yes, but it sounds like:

I'll call you back when I get good and ready, so don't hold your breath.

i.e., rather insulting.

Sorry...Here's the context:

My mom called me and asked me why I had called her.

I told her I needed to ask her something, but I forgot what it was.

And I said:

"I'll call you when I think of it."

PreciousJonesI told her I needed to ask her something, but I forgot what it was. And I said:"I'll call you when I think of it."

I hope this gives you a lesson in the importance of providing the context when you ask a question. After all, no one here is a mind reader.

So it is correctly used and I wasn't being a rude b*tch?

Aha! In that context it makes sense. It's correct. I would have included 'back' because it's a return call.

I'll call you back when I think of it.

CJ