I called my bionic from a land line, but hung up before I answered. Almost immediately, I got a notification of a missed call, but no led. I turned off my screen and the led started blinking and blinked until I turned the screen back on. Then it stopped. I think the point is that when the screen is on, you have a notification so you don't need the led. When the screen is off, you can't see a notification, so the led blinks. Until you clear the notification, the led will blink when phone is in sleep mode. This behavior started with Gingerbread.