My mom and dad as well as my aunt and uncle in law (they all are on one account, 4 lines) have been looking for new phone plans as they do it every couple years to take advantage of good phone deals. I recently saw T-Mobile offer a free iPhone 13 when you open a new line with porting a number, no trade in required. My dad, aunt and uncle have older iPhones that they'd be more than willing to trade in, but my mom has a 13 Pro Max that she would like to keep and trade it in for a 16 Pro Max later on. (likes pro maxes also why would she trade in the better 13 Pro for a reg 13.)

Although an option is for my mom to just not get the deal, it would be stupid to turn down a free iPhone. Could she get the iPhone and then switch her line back to her 13 Pro Max? She's not selling it and wants to give it to my brother. Or would doing this be effectively "cancelling" and they'd have to pay for the iPhone in full? Would appreciate some help.

On legacy T-Mobile plan (Magenta) that is a great deal. I see a ton of new iPhone deals for NEW customers, but how often do they come around for EXISTING customers?

I know the best deals are typically for new customers but does T-Mobile ever do Pro series deals when a new iPhone series comes out (say when iPhone 17 comes out...is it likely iPhone 16 Pro Max deals will become available for existing customers)?

thought about switching to a different carrier to take advantage of their new customer deals but the monthly fees are so high for most it would be a wash over 2-3 years staying with them, all while losing my T-Mobile plan (4 lines for $100, taxes and fees included).

Edit. Messaged t force and they gave us an additional 250 off of our order of two phones, so 125 per line.