[gruturo]

The SAT (SIM Application Toolkit) is... surprise, on the SIM card itself. It won't go away when flashing a new ROM - it will appear in any SAT-aware phone you stick the SIM into - even a 10 year old feature phone. It's mainly a relic of the noughties and dumbphones, think of it as a simple menu wrapper system which can compose and fire off Short Messages and USSD (xx#) codes on your behalf, so you don't have to remember that 101# is "check my credit" (varies by operator and country, there's no standard). They have some useful stuff (menus and shortcuts to check your balance or control functions like voice mail or sms-to-fax ), lots of less useful stuff (news, sports, weather etc.) and of course sleazier operators love to include menu entries which will fire off non-free SMS or subscribe you to crap without you realizing it.