Agree with that Crow Sister: one reason that folk shout into their mobile phones is that they can't hear themselves speak over the noise the bus itself is making! So any piped music would have to be loud to overcome background noise.
Just don't need it!
Occasionally, if I remember, I'll take my Ipod on longer journeys, then I can have the music I like.

Having said that we did once play live music all the way from Edinburgh to London on a train, even dancing in the aisles! Our party occupied most of one carriage, but anyone coming through on the way to the buffet car looked a bit bemused!