What if, and I'm just wildly speculating here, one very large client were able to offer them a higher a rate for exclusive access,
Typically, laws that establish regulatory monopolies explicitly forbid such exclusivity contracts. The first such example I can think of is railroad. When the US government was funding the expansion of the railroad, it was critical that the railroads would allowed anyone to ship goods. An exclusive contract that says "I will pay you double if you ship my goods, at the exclusion of my competitors goods" was bad for the country. This was basically the first "network neutrality" law. The only mistake they made was that the company laying the tracks was the same company that ran the trains. Oops. At the time it made sense.
I mean, it's a lovely optimistic view of the free market you have, but I think you aren't seeing all the angles.
Suggestion: Don't add things like "I don't think you understand" or "you are so naive" or "you aren't seeing all the angles" to your post. Let you point stand on its merits. You can get away with that as an AC on Slashdot, but you will quickly get booted out of a real-world meeting for that kind of attitude. Best to learn that lesson here. Often times you will say that then realize you are talking to an expert on the subject who has already heard your objection before and addressed it 20 years ago.
You were under the mistaken assumption that I came up with this idea just now. Don't try to be clever and shoot it down quickly without realizing that this problem has been known and understood for hundreds of years.
When establishing a monopoly, such as transit, power, or telephony, there are some lessons we humans should have learned. One is to create the monopoly over just the one thing you intend. Ex: If the problem is laying track, then make a monopoly to lay track. If the problem is laying utility wires, make a monopoly to run wires. Often times we forget that, and instead make a monopoly over transporting goods + laying track, or providing phone service + running wires, or providing power + maintaining power lines. Usually, we learn our lesson some decades later. Some times this happens because we can't imagine those things being separated until the technology comes along. "What, you could have 10 different train companies running over one set of tracks! Trains would collide! That's dangerous!" Or imagine this one: "How could you have *multiple* phone companies cooperating over one set of lines? How would the telephone switchboard operators share the lines? That's crazy." Then, computers and packet-switched networks were invented. Oh, and there was the old "Only the phone company can sell phones! If other companies made phones, they could damage the phone lines!"
One that we still come across today is "How could you have multiple internet service providers one one wire?" (sigh)
Many states learned this lesson with electricity generation. I live it Maryland and they finally decided that the "power company" should not be a company that provides power, runs lines, and bills customers. So Baltimore Gas and Electric was split apart into two companies. Unfortunately, one company bought the other -- that's another loophole to get around. If you split a company, forbid one from buying the other, or merging, or some workaround like that.
We sorta learned this with telephony when we split up Bell Telephone. But they also all merged back together until there is really only 3 of them or so now. Instead, we should have a local monopoly who builds and maintains telephone wires, and separate companies who provide the services that run on the wires. Otherwise, the company will make barriers to prevent other services from running on the wires. (Which is what is happening in this article.) Unfortunately, our telecom regulation doesn't quite do it right. (They half-heartedly tried. Some states tried laws that required the telephone monopoly to lease out their lines to small telecom companies, and required that they be allowed to co-locate their equipment in the central office. But the telephone company made enough barriers to slowly run those companies out of business.)
Anyway, this is a complex subject. This body of knowledge has been around 100 years, and any objections you or I come up with right now were probably already considered decades ago. Really, the point of my post was not to propose a new solution, but to say: Learn from history and follow best practices. There is a free market solution, and it does work, just implement it. (It's hard - how do you get enough political clout to tell a 180 billion dollar company like AT&T that they need to split up?)