That letter is so ridiculous that it almost seems like it was lifted from the parody letters page in "viz" magazine...
Nonsense of course, 20 occasions in 6 days? What absolute tripe. Letters like this of course require no proof or evidence to back them up.
Being caught using a mobile or any electronic device, barring very exceptional mitigating circumstances is pretty much a dismissal offence and rightly so, the notion that BTP should should storm cabs on a random basis to search for a phone is laughable, particularly as we are issued one as part of our drivers equipment
It's a an unnecessary slur on the professionalism of drivers and sounds very much like the politics of envy to me.