Technically this is already supported via the GSM standard. For example here is a Lithuanian company that lets you roam while there on their network without changing your SIM or paying your providers roaming fees:
The issue is that getting phone providers to co-operate is basically impossible. Not just politics, but everyone has their own way of doing things, so you need a custom implementation for each provider.
(Source: I used to work at an company who ran an SMS gateway)
https://widerfi.com/
The issue is that getting phone providers to co-operate is basically impossible. Not just politics, but everyone has their own way of doing things, so you need a custom implementation for each provider.
(Source: I used to work at an company who ran an SMS gateway)