Esta fue la solución que me dieron a mí por tener un problema similar: This is how I figured it out.*It worked for me anyway...The voice commands "reject" and "answer" worked when I unchecked the "sound and vibration" feature.Go to settings, Sound, under "ringtones and notifications" uncheck "sound and vibration".I told Samsung tech support level 2 about this issue.Annoying, I know....Good luck*
Ahora con Jellybean tambien en personalización más ajustes tener habilitada la opción modo bloqueo.