In the interim, while waiting for the Project FI sim to arrive and the old phone number to be transferred to the new FI sim, I cut down the old micro sim with a Fosom nano sim cutter from Amazon ($6.99).

It has adapters to hit the nano sim to each of the larger sizes to fit other phones.

Like most tools, it is fool-proof but not idiot-proof. As with any tool, look first, then “cut”. It’s easy and there was not a problem with the T-Mobile micro sim being too thick. (In which case you’d need to scrape the back with an emery stick.

Everything worked right off.