Using a mobile whie airborne is illegal - and flags up because it locks onto numerous relay stations instead of just one. Make a habit of this and you're likely to be traced, and when caught you'll not get a slap on the wrist. Breaking the Wireless Telegraphy regs is treated very seriously, and would likely involve a seperate action from the CAA for all the other offences/safety breaches you've committed.
As for the irresponsibility - the utter stupidity of doing this while flying - well, my mind just boggles. Listening to music ditto. If you think it's OK to do this what other idiocy do you indulge in whilst flying? Which of the other rules and regs do you think you can arbitarily exempt yourself from? What's up with an ego so huge and self-obsessed that it thinks it needs to make a telephone call from an aeroplane, instead of waiting a few minutes?
Saaad.
I can only say that I hope and pray you'll be caught. People who do this sort of thing are just not responsible enough the be allowed within a country mile of an aeroplane.
It's no wonder PPLs sometimes get a bad reputation when this sort of thing is being discussed on a "Professional" pilot's forum. Shame on you.