You wouldn't pay $10 while you are using your own phone. Since you have no EIP, you just upgrade to a new phone at any time. While you are paying that EIP, then you would have to pay the $10 fee per month if you want to upgrade again in 6 months.
Yeah, I get it. Was just wondering about this.
I think in principle this is a good idea. Say you would want to stay with Tmobile forever (i.e. more than two years):
Without Jump, if you want a new phone after two years, you have to make a new down payment and continue to pay $20 a month.
With Jump, you will keep paying $30 a month, but you get to upgrade your phone every six month roughly. For those who care about having the latest tech, this might be a good thing. The main issue I see is when phones have different down payments, e.g. if you want an iPhone with more storage: Do you have to cover the difference in down payment in addition to the $10/month? Are there different classes of phones?
Honestly at this point I still prefer the "bring your own phone" option. I can decide if I want a cheaper or a more expensive phone, I can decide when I want to upgrade, or save some money and stick with my older model for longer.