That's ridiculous, thanks I learnt something today. It’s essentially running like a VPN though so how do you access local websites and services in the foreign country that require a local IP
Yeah it's pretty much essentially like a VPN. This might be advantageous or it could be a problem. If you want to watch dstv while abroad you can just pop in your SA sim card and its not a problem. But if you need to use a local site that geo restricts you'll have use a vpn or connect to a local wifi.
But this all came about because "back in the day" the home networks never had real time insight into how much data customers were using when they were roaming. They would just receive a bill weeks or months later from the other wireless carrier and they would be on the hook if their customer can't pay or won't pay R100000 for watching a Netflix video. But when things are routed via the home network they can just setup a firewall rule to drop packets if a customer exceeds some predefined spending limit.