I've been using TMobile for quite a number of years, now the plan I have is one of their grandfathered plans.
I can buy minutes, $100, get their Gold status, which means all minutes are valid for a year. Once the year is up, I can top up for $10, which will extend the expiration of all minutes another year.
Pretty good deal.
Currently, TMobile has this plan
https://prepaid-phones.t-mobile.com/pay-as-you-go $3/mo, which isn't too bad