Nice report.
Actually, the $19.99 unlimited data add on has been mentioned in a number of threads. Unfortunately, they are stopping the data plan next month.
http://gadgetblips.com/story/at_t_to...one_data_plan/
Phones: Xiaomi Mi Mix 2, Samsung Galaxy A50, ASUS zenfone 3,
Sim cards: AT&T (Contract), 3 UK, Piranha Mobile