Let's say Congress decided that it would make sense for highspeed (truly highspeed -- at least 45 Mbps both up and down, not 200 Kbps) access to the internet to be considered a public utility.  (Public utilities are subject to rate control.  Their earnings are established by a public commission.) 

Such a decision would clearly advance a legitimate government interest.  Indeed, the current Administration has said that broadband access for all is a crucial government policy.  Congress would be saying that beachfront property should allow reasonable access to the ocean -- the self-owned commons -- and there are some nice beachfront cases that Congress could rely on here.

Now, the companies that have built fiber networks in the U.S. would quickly claim that such a Congressional action would constitute a "taking," because they wouldn't be able to charge premium rates for each service an end user wanted.

Our government can regulate private property, as long as it does so for public purposes, and as long as it acts reasonably/fairly/justly.  But there are limits in the Fifth Amendment on what the government can do.  That Amendment says that private property can't be taken without just compensation. 

A unconstitutional "taking" can happen when the government physically appropriates private property or deprives its owner of all beneficial or economically productive use of it.  That wouldn't be happening here.  The Baby Bells would still be running these access points, presumably, and making some market rate for doing so.  Indeed, they could use this access to sell their own content services to customers. 

In the absence of this kind of categorical action, which is unquestionably a "taking," you have to analyze the economic impact of the government step to see whether compensation is required.  The Baby Bells would have a strong argument that their reasonable "investment-backed expectations" had been stymied by Congress. 

But there would be a very strong response that they have plenty of money to keep going (a fair return!), and that they'll be able to raise investment money based on their other businesses (including their competing IPTV business).  Mere economic impact isn't enough to make something a taking, and the Bells can't have expected that they'd be allowed to monetize all this access.  No explicit government guarantee was ever provided along these lines.

Without doubt, the Baby Bells will say that a "fair market" price doesn't capture their immense investments in fiber.  They'll also claim that they're being denied the opportunity to make an enormous amount of money, and that anything short of that enormous amount of money makes any regulation an unconstitutional taking.

The Baby Bells might even claim that providing highspeed access in a regulated fashion is going to be such an unprofitable business that they'll have to stop providing this access.  This would be their death threat:  allow us to reap all the profits we can, or we'll rip out the fiber and leave the U.S. in the dark ages.  But existing case law establishes that they can be forced to continue to run this unprofitable arm of their business, as long as they are profitable businesses as a whole (including phone services, equipment sales, etc.)

So, if they stayed in business, in the now-regulated highspeed access business, they might have to operate that business at a loss.  That's the way it goes. No taking has happened, according to a long line of cases. 

If they said they had to go out of business as a whole, or if for some reason Congress decided to simply convey the highspeed access business to someone else to prevent it from being abandoned, the Baby Bells wouldn't get all possible future profits.  They'd get whatever a willing buyer would pay for the networks they had built -- their salvage value.  This would be litigated for years, but in the end there would be a number.

So -- if we regulated access, it probably wouldn't be a taking.  If it was a taking, we could pay them back.

Maybe we should take it.