Regardless of the QNH issue, I have lost track of the number of times that crews state the current ATIS and have ignored half of it by calling the wrong freq, or asking for Pre departure clearance when the ATIS says it isn't available, or...... I could go on. From our end it often appears crews only wait for the letter then stop listening.
Surely it can't be too hard to acknowledge the letter, QNH, aircraft type and stand on first call to GMP. It certainly saves R/T when we don't have to go back and ask for it all again.