In message , Brian Watson
writes

It's because

1) *y o u a r e u n d e r g r o u n d* and there are usually at least a
few yards of earth between you and the mast, also

2) People don't want to hear you shouting, "I AM ON THE TRAIN" over the
racket of a tube train so no-one is going to go to the expense of enabling
it.

I never cease to be amazed at the number of phones users who shout down
their mobiles "Hello, hello! Can't you hear me?" as the Piccadilly
plunges down to the depths after Baron's Court. I guess they never
studied physics.
--
Paul Terry