There is two ways to block incoming numbers, from server
level (t-Mobile) then the person of interest will know that you blocked
incoming calls from that specific number because t mo will put recording
"person you trying to reach has blocked incoming calls" or something
like that. Second way from your device add number to contact list then tap the contact
and hold until menu pups up , select add to reject list and done, every time that person calls will be redirected
to voicemail and won't know that you blocking anything. To remove number from rejected list go to contact tap menu and select remove from rejected list.