68+iou1 - there are plenty of Captains that do the same. I've even seen some making calls during the taxi...
Lots of people interrupt our procedures on the flight deck during preparation for flight. I try not to let it bother me too much, but when it is obvious that you are both in the middle of the performance calculation or a checklist, I would think it is good manners (wherever you are from) to wait 30seconds for it to be finished. Even if you do have a short turnaround, nothing is that important to risk making a major error just to avoid upsetting an engineer or the dispatcher. We are all in control of whether we choose to respond or not and in my experience the majority of pilots are quite prepared to allow themselves to be interrupted during critical stages of flight preparation.
I have found the phrase "I'm so sorry, I do apologise for talking while you were trying to interrupt me" quite useful for those who persist....