Here's saying if you own the whole system you can optimize things to be more efficient than if you have a ton of separation between the people who run the different pieces of the system.

So in the this case maybe AT&T having vertical integration is a good thing.

Personally I haven't seen any positives for consumers from Comcast buying NBC Universal so I don't see how this would benefit consumers either.

Sorry, but these two systems are incomparable because you just do not run any random train on the railway.

If you would like to find something that is comparable, I'll recommend to look for it related to the roads.

Try to imagine a situation were single private company owns all the roads (of one region), including all the highways and local roads and has also a bus company.