It uses tmobiles network. I actually have this sim. They were giving it away for free, and it came with $10 credit and free shipping, so I decided to try it out. They also happen to have good international rates generally besides the excellent rates to S. America. For example, it's only 26 cents to callk a UK mobile and 1.5 cents to a UK landline. Plus airtime of course. My brother used this sim without any problems when he visited from the UK last month.
Info about the free sim:
http://www.howardforums.com/showthre...ht=tuyo+mobile
Rates
http://www.tuyo.com/rates/intrates.a...loc=&slocid=44
Phones: Xiaomi Mi Mix 2, Samsung Galaxy A50, ASUS zenfone 3,
Sim cards: AT&T (Contract), 3 UK, Piranha Mobile