It is easy to criticize, however, and hard to propose a more reasonable alternative. The fact is that carriers are saying they will provide feedback to users about how much data they have "used" along with warnings when they're about to exceed the plan amount. Also, bytes, like minutes for phone plans (as in, used for talking), are fairly easy for users to understand and carriers to monitor. The more data you send and receive, the more you pay. Carriers, for their part, need to track usage as part of normal operations to ensure their network is balanced, anyway, so why not report those data to users. Its simple, in concept. How else should usage be tracked if not by byte?
So, what if we came up with a way to meter the bill based on something that's focussed on user experience? The primary complaints customers have, and the primary challenges of a carrier, are capacity and availability. If there are great connections all over a city but poor connections outside the city, what happens when you're driving or taking the train home for the evening? Your call gets dropped and your files start downloading slowly. So, why should you pay the same price while you're in a bad area as you do in a good area? Reversing the scenario, what load (and therefore cost to the carrier) do you put on the network when you're in an office building where the signal doesn't penetrate? How about when your phone is powered off? None. The carrier allocates zero wireless capacity resources to you when you're off the grid. So, why should you be paying at all for the significant portion of the day when you're not able to use the service? I suggest billing based on two factors: 1) The Carrier's quality of service to the user (i.e. speed and latency) and 2) The portion of time that service is available to the user (availability). The better job the Carrier does, the greater proportion of the plan fee they can charge their customer at the end of the month.
As with any idea, the implementation details determine everything. I'm not advocating making the wireless business so volatile that carriers can hardly stay in business. Reasonable limits should be in place such that customers have a minimum fee to pay, even if they choose to turn their phone off all month. There are some costs to having the network available to you, even if you don't choose to use it. Likewise, reasonable limits should be in place on how much the carrier can charge if they achieve 99.99% coverage, quality, and reliability. That maximum amount should be known and agreed to when the plan is purchased. Carriers should publish their quality and reliability numbers, by area, every month with history reported for at least the length of the longest contract offered, so that customers can make informed choices when selecting their carrier.
This approach has merits for the customer in that it re-balances power such that more is in hands of customers and it gives carriers an immediate and continuing incentive to improve the customer experience. It also gets the industry away from billing customers for a commodity that has no direct link to cost - bytes - and which customers have little to no control over (web pages don't tell you how big they are before you load them!). Instead, the industry moves towards billing for the primary cost drivers - capacity and availability. Carriers who provide a better experience by expanding and balancing their networks better make more money. Customers pay for availability at an agreed quality level.