The OnePlus 6T is the first OnePlus device to penetrate the US market through carriers and the T-Mobile is the first one to offer it. But just like every other Android device sold by the US carriers, there are some restrictions that you need to keep in mind.
For starters, the carrier will only be offering the OnePlus 6T in Mirror Black variant featuring 8GB of RAM and 128GB of storage for $579 or $24.17 in monthly payments, respectively. If you don’t need the extra RAM or the storage falls short, you will have to get it from OnePlus’ official web store.
But not all is bad as T-Mobile is offering a pretty sweet deal with its exchange program – $300 off if you trade-in an eligible OnePlus smartphone. And that means all OnePlus smartphones since the first generation, presumably if your old handset is in good working condition.
Also, T-Mobile can unlock your phone and let you use it with other carriers as long as you’ve been connected to their network for at least 40 consecutive days and you’ve paid off the remaining balance before the contract ends.
And now some bad news. T-Mobile OnePlus 6T devices won’t be able to participate in the OxygenOS Open Beta program and uninstall the additional software that T-Mobile pre-loads. On the other hand, the bloatware is pretty limited compared to other devices. We are referring to the Unlock app (for network unlocking) and the T-Mobile account manager app. According to a Reddit post, there’s a way to uninstall the other two apps: Name ID and Visual Voicemail.
Source | Source 2