@Jean *************
Not exactly but probably the easiest way to see the
Point
In most of the world , phones are not necessarily locked to one carrier and can have more than one SIM card or equivalent eSIM or a combination of both
Allowing the subscriber to add another SIM for the past decade or so, but…
Some carriers ( and by that I mean all carriers in USA lock still lock any phone that you buy directly from them )
They will usually unlock your phone, but often it takes x number if business days … blah blah blah. During which time you spend $10.00+ per day. In roaming fees if you answer an SMS or phone call