Is it correct to say "will call once I get back"? [closed]
Yes.
However, in doing so, be warned that you are also
a.) promising to return, soon;
b.) promising to call as soon as you return. (where as soon as you return means within 1/10th of the time you have been gone, dating from this message).
Promises are legally actionable in many Anglophone jurisdictions.
I will call you as soon as I am back or I will call you as soon as I get back are more correct versions of the sentence.