@weebull @isleofmandan @neil

"When a customer of one CP calls a UK geographic telephone number on another network, the calling customer's CP pays a wholesale charge to the called customer's network to complete the call." https://www.ofcom.org.uk/phones-and-broadband/phone-numbers/fair-reasonable-charges/

CP = communications provider

Those charges, including the per-minute element, were the key revenue stream AFAIK.