in a long time/ for a long time

Hello there!
Thanks for your quick response to my last posting!

I've got another question related to the prepostion.

* I haven't heard from you in a long time. *

Is the sentence correct?
As I know, "for a long time" should be the correct phrase.
I mean... [I have seen the movie in a long time.] sounds alright but the sentence above doesn't.

Do the two phrases --in a long time / for a long time -- have same meaning and no difference??

Thanks!

[Tdol]

They do and both are used, though 'in' is more colloquial.