If you don't mind me asking, doesn't that get quite spendy and it would seem like JUMP would be perfect for you if T-Mobile is your network. Not for the phones you keep or give as gifts, but if you are trading in phones with your carrier for new phones, don't you have to pay off the full price of the old phone first and then maybe even a down payment on the new one?
I don't mind you asking and yes, it can get somewhat spendy! It can get kind of complicated to explain without giving the whole long story, but this is a summary (I hope). I budget for the phones that I think will come out the next year in the fall. I have multiple lines on T-Mobile and AT&T. I don't like to buy T-Mobile phones as much just because I don't like certain things that T-Mobile does as a business. I prefer their service prices, not their devices. I buy a mix of carrier devices and unlocked devices. So this alone makes JUMP unappealing to me.
I keep my devices as part of my self-insurance program, so I don't use carrier insurance for either carrier. This is another strike against JUMP. Also, JUMP requires that the customer be on the Simple Choice plan. If I converted to Simple Choice I would spend $20 more a month on service alone than what I spend now, which is another strike. Also, I don't care to use the EIP for the phones. I just buy them outright and this is another strike against JUMP.
That's four strikes against JUMP so it's more than out as an option for me.
As for the old phones, I keep them until I think that they are no longer working properly. Two of the phones that I traded in a couple of months ago had excessive battery drain (1% or more per minute) and one was just a cheap phone for me to familiarize myself with the OS. I thought that the $100 that I got for each phone was probably more than what I would have gotten on the secondary market, so I went for the trade-in.