So, I have an iPhone 6 that was previously on my account, am currently using a 6S plus on a device payment plan. Could I add my old IPhone 6 as a new line on my account and then trade it in for a new 7?. Would I have to activate it in my name?
You could, but do you need another line? To get the FULL $650 credit, that line would have to be active for 24 months. Seems like a lot to do for that credit. Possibly you don't realize that "up to $650 credit" is a MONTHLY credit credited to your account each month to offset the monthly payment on a DPP purchase. Once you cancel the line and no longer have it active, the full amount becomes due and you would no longer get that monthly credit on your account.
I just thought once I owned it, I could transfer that phone to my daughters line, but if I need to keep the actual line active for 2 years, it wouldn't be worth the trouble