I don't know about that, here is more info:

https://www.pine64.org/2020/01/24/setting-the-record-straigh...

> In short, unless you explicitly send data to the modem, it is never in contact with the blobs running inside it. The modem cannot send any data to the phone unless phone is willing to receive it

I guess there are some legal concerns with open source modems

http://wiki.openmoko.org/wiki/Open_GSM_modem

You can't disable STK applications: They are an integral part of the SIM card. If anything, you could hide the user-facing icon, but that wouldn't do anything about any background processing the applications might be doing.

However, they can only interact with the baseband in any case: While that still allows extensive tracking and potential mischief (like making expensive calls on your behalf), this is nothing your phone provider can't already do, i.e. knowing where you are and bill you arbitrary amounts for services you might not have initiated (when on postpaid).