I've a rooted phone (Samsung Grand Prime, without CM, just the STOCK Rom), and what I want to know if it's possible with Android 5.0 phone or newer to block calls without ringing. By default, the Call Rejection List just wait 1 ring before reject the call... All blocking applications has to wait 1 ring too before blocking the call, which is logical. But the main drawback of this is that people could suppose if they're blocked.
I've tried two applications : RBC & Call Master that do this stuff (they need root permissions) but each shutdown the mobile network and don't seem to work well witht Lolipop or newer.
I've read somewhere that since Gingerbread, Google don't allow applications to get the MODIFY_PHONE_STATE, so just only apps that need root could do it.