How do I figure out how much I have to put down for a new phone?

My carrier is T-Mobile. My aunt is going to take over payments on my current phone for her daughter, and I'm going to get an IPhone 7+. So I was just wondering if there's a way I can figure out how much I'm going to have to pay right away?

Just talk to the clerk

Hi so you need to set up a separate contract for the new phone.