Well this is nice of T-Mobile and shows they do somewhat care about customer service. I can chime in and add my experience with the English (American?) division of T-Mobile: they responded to a mention at a social network while I was not even really meaning to ask them a question, I merely mentioned them. The Dutch division is not as great, but oh well.
Still, I'd say it's how it's supposed to be. In the Netherlands it'd be illegal to upgrade contracts like this. You can't start charging more without giving the user an option to quit the contract for free (or continue the old contract for the old price). Also after the contract period (one or two years), consumers have a right to cancel the contract each month, also for free.
They didn't start charging more. Telecom companies pull some shady tricks with plans and billing, but increasing the monthly fee without notice part way through your contract is not one of them.
He signed a contract for some period of time, and it wasn't up yet. After it was up, he would have had the option of one of the new plans, or switching providers, just like everyone else does.
With mobile providers in the US, if you don't use your "upgrade" you can keep using the service with no contract. If you accept their upgrade, an offer of getting a new phone at discount, you lock yourself in for another year.
Still, I'd say it's how it's supposed to be. In the Netherlands it'd be illegal to upgrade contracts like this. You can't start charging more without giving the user an option to quit the contract for free (or continue the old contract for the old price). Also after the contract period (one or two years), consumers have a right to cancel the contract each month, also for free.