Nothing new
T-Mobile have had restrictions on VoIP for ages - depending on the package you paid for you may or may not be able to use it. Not really any different to the restrictions on using mobile data only from the phone, instead of as a modem.
Just to point out to Mectron and others - it's their network, they can make any rules they like. And if they choose to make certain services only available to customers paying extra, that's their business.
Actually Mectron, you're an idiot. They aren't restricting software on 'your' hardware, they're restricting network usage. Very different, and perfectly OK. And that rant about paying for unrestricted pipes and all those punishments you'd like is just wrong. I'd almost suspect a troll...
I could *maybe* see a problem if the restriction was on a particular application provider but a blanket block (as exists) doesn't seem such a big deal - they've decided they don't want something on their network and that's it. Or alternatively (depending on provider) you could always pay the premium and be allowed to used the technology.
Personally I have a contract with a very fat 'fair use' limit which explicitly allows VoIP so I don't have any problems!