Unfortunately, T-Mobile, like every other mobile phone provider, has a mandatory binding arbitration clause. It does come with an opt-out provision but requires that someone have opted out within 30 days of the first time they opened their account. If a subscriber did not opt-out back then, even if the terms and conditions subsequently change, the agreement is very specific that a new opt-out opportunity is not created.

I opted-out when I signed up a decade ago but I have no proof of having done that other than a website I barely remember visiting. They do not display my opt-out status anywhere and customer service claims they have no access to know whether or not I did.