Do you have a contract? That maybe why price you pay is cheaper.
Seems like parent was only in US for a short period of time, so he probably didn't wanted to sign a, say 12 months, contract.
http://consumerist.com/2013/06/07/t-mobile-has-a-30-unlimite...
http://www.walmart.com/ip/T-Mobile-SIM-Kit/24099996
http://www.walmart.com/ip/Tmobile-30-Wireless-Airtime-Card/1...
T-Mobile is about the same as Sprint and AT&T, and all are sub-par to Verizon. But what's nice about T-Mobile is that you get unlimited data, whereas with Verizon, you'd better cash in your fleet of 777s to afford your bill.
Sheesh.