I noticed in some of the example applications on the repo (Google OTP, Secure File Manager), they require a custom Java applet to be installed on the Java card. But Java applets cannot be installed on network provided SIMs/UICCs typically since they are locked down.
My understanding is that a unlocked Java card needs to be used. But then how can you use the phone with a 3rd party mobile network (E.g. ATT)? Is it possible to provision a UICC with a custom applet and still use it with a 3rd party network like ATT?