They're largely not charging end users for it anymore because the cost is just too low these days, true, but as I understand that's still how the pricing model

They're largely not charging end users for it anymore because the cost is just too low these days, true, but as I understand that's still how the pricing model evolved. > you can keep your same mobile number when you change carriers no matter what the original region was Yes, but only because all carriers have physical or at least logical/rented infrastructure in effectively all "rate centers" [1]. The call still goes to whatever rate center your number corresponds to (barring other agreements, I assume, e.g. the originating and terminating carrier having VoIP interconnectivity). That's very different in countries that have dedicated prefixes for mobile numbers: The originating carrier can immediately detect the target network (instead of target region) from the prefix and route the call to the nearest interconnection point between the two. This means that the terminating carrier usually carries the traffic for the longest geographic stretch, something for which they usually/historically got to bill the originating carrier via interconnection fees. Today, these fees are either gone or nominal/heavily regulated, but the more efficient routing is still a factor for reliability. [1] https://en.wikipedia.org/wiki/Rate_center https://en.wikipedia.org/wiki/Rate_center