Earlier quoted context omitted.
Even less if you don't talk much: http://prepaid-phones.t-mobile.com/prepaid-plans ($30/m for 5GB of 4G, unlimited text, 100 minutes)
I'm always worried that someone at T-Mobile will notice that plan, say "whoa, how did that get there?", and delete it. It's just so much cheaper than everything else on the market.
Note that in ordering the SIM card I did not indicate that I wanted any particular plan. The $30 plan just "happened" to be available for that card.
Was I willing to wait for one week in order to lower the bill for a large recurring cost by 40%? Yes. But T-Mobile seems to be gambling that most people aren't.