The cheapest PAYG contract offered by BT's subsidiary EE gets you 500 minutes of phone calls for 10 pounds. Which also buys you 10GB of internet and unlimited texts.
Meanwhile, 500 minutes of phone calls from a BT payphone would set you back 250 pounds!
So, it's obviously not the poor who benefits from pay phones. Except maybe a subset of homeless people who can't commit to a PAYG contract. Seems like it'd be more economical for BT/EE to just handout phones at homeless shelters and shutdown this ridiculous relic.
https://shop.ee.co.uk/sim-only/pay-as-you-go-phones
https://www.bt.com/pricing/current/Call_Charges_boo/3545_d0e...