Carriers charge us for every single thing they can, call minutes, SMS messages, megabytes of data, new phones, changing phones, changing plans, everything. They have so many different items to charge you with that when they add the monthly total you have no idea what you're paying for. So far this has worked great for them, people need connectivity and with limited choices you're probably stuck having to choose from one of the big 4 to be your provider. This means that they can offer you what you want but tied to the stuff you don't want, and you have no choice but to go with it. We all want more data and less voice and SMS but you can't have a data-only plan, at most you get an unlimited anything but the cost of those plans are still a mix of data, voice and SMS plus a few extra fees you don't even know why they exist.
As more and more people depend more on data and less on voice and SMS, someone will eventually create a data-only plan, maybe it's one of the big 4 or maybe it's a smaller, regional carrier but the fact is that someone will eventually do it. That's the moment carriers start losing control over how much they can charge users.
If one of the big 4 carriers begins offering a data-only plan, the other 3 will have to do it as well to compete with it. If a small regional carriers does it, the amount of people jumping aboard those plans would still force the big ones to offer the same kind of deals. That means that users will be paying just for data, no calls, no SMS and the math would be much simpler, it's just one item on the bill. These leaves carriers with just two ways of competing: speed and price. They can offer more speed for the same price, or they can offer the same speed for less price. Either way, consumers win and that's what scares the carriers the most. Consumers will begin to take control of their devices and their IDs, since it's data-only, phone numbers will eventually cease to exist and we'll all be known just by our names or email addresses. People will be able to switch carriers like they change clothes because they wouldn't even need to take their numbers elsewhere, it's just data. Carriers would become the dumb pipes we want them to be with just price, speed and coverage to differentiate from one another. The sooner we can get to this future, the sooner the prices will go down for everyone.
If there's one thing I'm sure of is that it's not a matter of if this happens, it's a matter of when it happens.