[SOLVED] Find busy line while calling with Asterisk

I am using this code for making a call with Asterisk:

exec("DIAL", "DAHDI/g0/" + phoneNo + "," + timeOut + ",mg,");

But this snippet always return 0.
How can I find the phone line is busy or not answered?

First i have inform you that that line return 1 if dial can't be done(but yes, that is rare situation).

For result please check dial command page:

It return DIALSTATUS dialplan variable.