oretoz 16 hours ago

There is an API available from many mobile operators called SIM Swap that can be called to find out if the SIM has been swapped. Often these calls are made by Banks to an aggregator (such as Telesign or Twilio) that finds out the mobile operator (e.g. Verizon or AT&T) that the customer belongs to and calls SIM Swap API on that operator. There is currently no universal app for that purpose but it can be developed. See CAMARA Project for latest specifications of this and many other APIs.

AStonesThrow 19 hours ago

Just a point of jargon: "SIM swapping" commonly refers to the scam where criminals usurp someone's mobile account by swapping the phone number to an attacker-controlled SIM card already installed in a separate, attacker-controlled mobile device.

The physical act of removing one SIM card, and/or inserting another, into a mobile device, often for legitimate purposes, may also be "SIM swapping" but I've striven to avoid using those words, due to confusion with criminal activity.