> No, upgrading the network allows you to serve more customers at higher cost (the cost of the upgrades)
Upgrades are a one-time cost. You charge a higher rate for access to the faster network until the investment is paid off then you phase down to all customers. Then your operating cost is lower per subscriber in the long run.
These days, upgrades are a continuous cost. By the time you've paid off an upgrade it's time to upgrade again. Charging a higher rate costs you customers, and with fewer customers you don't even need the extra capacity you just bought. Also many customers are on contracts so you can't increase rates right away.
In contrast, with pay-per-GB, upgrades increase revenue automatically without losing customers. You don't have to increase your rates and you can probably even decrease them and still increase revenue.
Upgrades are a one-time cost. You charge a higher rate for access to the faster network until the investment is paid off then you phase down to all customers. Then your operating cost is lower per subscriber in the long run.