T-Mobile isn’t technically a legal system so this is referring to them fining for illegal content of their own accord as part of the contractual arrangement. It’s not as if they impanel a jury :)
You can't be fined by a private company. They can include provisions in a contract that may lead to increased costs but this is something you would agree to beforehand.
Well, under the restatement (and case law in some states) a liquidated damages provision cannot represent a penalty. Instead, it has to represent an estimate of actual damages in breach, more or less.
Absent the actual language in the Agreement between T-Mobile and the intermediary providers like bandwidth.com, we have no idea what the penalty is called - bandwidth.com is calling it a “fine” but we don’t really know.