Regarding Phone Upgrafe

Buying devices on the payment plans can be pretty easy and convenient. Normally you would need to wait until the phone is fully paid off at the end of the 24 months before you can use it as a trade in. We do have a Jump! feature that you can add to your line that has a lot of helpful benefits. One benefit is that it allows you to upgrade your phone after you pay off half of the retail price. That usually falls at 12 months unless you had to make any kind of downpayment. 

The way it works is when you make the payment to bring the balance down to half, you can shop for a new phone and choose the Jump! option in the order process. That flow will ask for your current phone information (make, model, IMEI) and lists it as the trade-in device. You complete the order by paying any taxes and downpayment necessary for the new phone. When you get the new phone (in the mail or at the store), you return your current phone and the system will pay off the second half of the current phone within a few days of T-Mobile receiving it. At the end of it all, you will only have one payment plan on the new phone. 

Hope this helps!