Trading in a locked T-Mo phone to Samsung?

[singelectric]

So... I've got a T-Mobile-purchased, carrier-locked Galaxy S9 that I got a year ago (when they offered me a $200 credit for a phone Galaxy S4 that was collecting dust in a drawer for years). Getting the $200 required me to pay for the device in monthly installments (getting a $8.34 credit a month for 24 months), and so there's still a balance on the device and it's still carrier-locked.

Samsung offered $550 for me to trade in my S9 and pre-order an S10. Their FAQ says:

"The device I’m trading in is one that I bought using an equal payment or other financing plan, and I still have payments left on it. Can I still trade it in?

Yes – however, please note that all remaining payments on the device you’re trading in are your responsibility. You may also be subject to additional fees. Check with your current carrier for details."​

I'm HOPING that T-Mobile will let me continue to make payments even though I won't be using that device, since I'll be sticking with their service. I don't think T-Mobile really cares what device I use (I went back to my old Pixel for a couple weeks by swapping SIMs and they didn't care), but I wasn't sure if they'd ding me for the remaining value for some reason - which would suck, since then I wouldn't get the full $200 in credits I'd been hoping for.

 

[singelectric]

And, to answer my own question, speaking to a T-Mobile rep, they confirmed that I can send in my device and continue to make EIP payments, however, the device will stay locked to T-Mobile.

 

[bkeaver]

So your trading a phone in that you are still paying on for another phone that your going to have to pay on as well???

Why would you do that....???