In message , at 11:09:30 on Sun, 14 Jul
2019, tim... remarked:

I'm not sure how many phones ever took the full size SIM.

Commercial considerations killed them off: the idea was that a person
would have a SIM, and be able to share/borrow a phone to use it in.

But the networks wanted to tie people into having their own phone
(and contract) in particular not wanting a phone they'd subsidised
being used with a SIM from a rival network,

They solved that problem by having phones "network" locked

My "acquired" smart phone still is

Is still what. Locked? That's hardly unusual.
--
Roland Perry