Yes, Simple Choice.Ive been able to buy 256gb iPhone Pro Max from T-Mobile before and was able to take advantage of the $1000 bill credits. the 256gb Pro max was $1200 so I just had to pay the $200+taxes up front.
Also I have 8 lines on Magenta Max (but only 4 people) and had no issues with anything (6 devices on EIP). Sorry but I dont know what you mean with this part: "Any deals I've ever found from my carrier (or other carriers) are outright assuming three or four lines max for a family." What t-mobile plan do you have? Simple Choice?
When I was looking up T-Mobile's 55+ plan (my wife had turned 55) I was informed that the deal was only for two lines and the primary line (which is me) had to be the person that was 55. At the time we had 8 lines, so we were told we didn't qualify.
I've seen a lot of prepaid or post paid family plan deals by other carriers where the special was only for 3 or 4 lines. If you had more than that you had to pay more. I'd expect that anyway (more lines), but at the promo price. That wasn't the case.
If I switched to Magenta (or Magenta Max) I'd lose a free line and my plan cost would increase.
Cool that you got a deal on a higher capacity phone. It happens, it's just not as common as deals for lower capacity devices.