T-mobile has a $3 per month flat rate plan that includes 30 minutes talk time or 30 texts. Additional minutes and texts are at the 10 cent rate.
I bought a burner and a card with minutes at a Best Buy and paid with cash. But I think any kiosk will work.
You can go into a T-Mobile store, but then they want to set you up as a customer. No thanks!
You can re-up your minutes with a credit card online, but that leaves a trail, of course.
There is a T-mobile app to track your minutes.
One thing that I dislike about T-mobile is that you don't get any warning when you are about to run out of credits. So, you can get cut off in mid-convo.