There are arguments both ways, but personally I think that NN is closer to the way to go. If an internet company wants to provide fancy search or movies or whatever, they shouldn't own the pipes. There's too much potential for abuse when a local for-profit quasi-monopoly owns a choke point.
There has been a long running tide of discontent towards Telstra for many years because of almost exactly this problem: they own the copper lines as well as sell services on top. It has taken legislation and court hearings to force them to allow other parties to sell access. Only a few years ago, the CEO of Telstra all but said that if he didn't have to sell wholesale access, he wouldn't. This was one of the reasons he is no longer CEO of Telstra.
Ever since Telstra was part privatised, the issue of separation of lines and services has never gone away. Many commentators said the government of the day should have split Telstra into a government org which owned the physical infrastructure everyone uses, and sole the other half as a services company just like everyone else. In the meantime, we had a change of government and the new lot seem to be heading down that road.
The monopoly of vertical integration is also why much of urban Australia got two cable networks a few decades ago: one from Telstra, one from Optus. Our population density was barely enough to support one, but two?
Wade.