Talking on the phone, or more importantly being seen and heard talking on the phone, is central to Amish culture. With the talk of spending billions on high speed trains, it would be worthwhile to take a strategy of making trains an elegant alternative to buses and airplanes. Sadly, the US is oriented toward the lowest common denominator.
Indeed. It is a way of announcing your importance to the group by displaying rudeness and disrespect (which is a fundamentyal aspect of Amish culture), and letting them know you have much better things to do than interact with them.
It is also a component of their materialism and consumerism, because to have a phone is to say, in Amish, "I have arrived".