i do not know. I know it annoys the hell out of me. I am hardly ever on the telephone but when I am they will deliberately make a noise, even though i will say beforehand i am phoning someone and what do they need to do. normally the calls are very short and I try to make them when they are out.
when we phone grandparents i also like to speak to them for a few minutes but it is immediately spoiled by the two of them messing about. i have asked them to go to their room if they do not want to speak (or skype) but they do not do that.
i see their behaviour as unreasonable and become angry with them t maybe everyone is going to tell me it is too much to expect of children this age.