>T-Mobile has always tried to separate itself from regular telecoms, but charging customers for essentially nothing doesn't sound very Uncarrier-like

It seems weird to call the process which is literally essential to using a device on the network "essentially nothing".

The unstated assumption might be that T-Mobile is charging for something that costs them nothing, but that also seems a little presumptuous. I assume there have to be some fixed costs associated with registering a device to properly authenticate with every bit of transmitter hardware on the network, plus KYC burdens - otherwise, T-Mobile has no incentive to introduce friction costs for new customers.