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"I can think of so many ways to solve this problem. But it's super hard to find any information if how this all works."

LTE and 3G solve the problem of authentication and encryption with the tower - the problem is that an attacker can, through interference or other means, force your handset to downgrade to 2G operation.

There is a very, very simple solution to this: display an icon/error when you downgrade to 2G and an even bigger icon when your 2G connection has no encryption (which is a valid option for a 2G connection).

This would be trivially simple but for reasons that are difficult to understand, phone OS and SIM providers do not do this.

"But it's super hard to find any information if how this all works."

I would recommend viewing/listening to the CCC (Congress) talks on GSM subjects that have been given over the last ten years. The osmocom "baseband-devel" is also a good mailing list to read the archives of ...