Apple to Release iPhone Update That Blocks Robocalls The feature is apart of the device's br iOS 13 software, which debuts br this September. To activate it, users must go br to the settings section br and select "phone." From there, they pick br "Silence Unknown Callers." This forces robocalls into voicemail, meaning your phone won't ring. There is a drawback if you are expecting br an important call as the feature br blocks all unknown numbers. Your caller will be able to leave a voicemail, br but if you want to answer right away br the update should be turned off.