[XaYdEk]

By sending binary SMSs. There are multiple classes of SMS, including binary messages through which operators can access and change data directly on your SIM. Since that's also your crypto chip, yeah ...

TLDR: https://www.contextis.com/resources/blog/binary-sms-old-back...

If you have a few days: http://www.tamps.cinvestav.mx/~vjsosa/clases/redes/Mobile%20...

Edit: You might find them referenced as silent SMSs, because you never see any indication of receiving it.