Well, FWIW, when I bought two SIM cards from T-Mobile online, they didn't have any micro Sims in stock, so I got regular full-size SIMs instead. I cut one of them down by hand with a sharp scissors and a template you can easily locate on the web. The other one I took to my local T-Mobile store and asked if they could swap it out for me (read online that they will often do this). Instead, he offered to cut it with a device that looks a bit like a hole punch and can be found online selling for around $10.
Pay-as-you-go SIMs and Micro SIMs are here
Prepaid Cell Phone Plans, No Annual Contract | Monthly4G | T-Mobile.