backlight goes out when recieving and making calls

Hi Hi,
So i have the same problem, have you tried shaking it and tilting it every which way. that normally works for me. I'm guessing your phone is fairly old.

When you are talking to someone normally, with your phone to your ear, then the proximity sensor kicks in (what Olvin said) and the screen turns off (the entire screen, not just the backlight). The sensor is to the left of the speaker, which is at the top of the phone. It was designed to conserve energy, because you can't see the screen when the phone is to your ear anyways. Simply move the phone away from your ear, which the sensor will detect, and the screen should redisplay.

When you are talking through speaker phone, the screen will turn off after ten or so seconds. Again, this is to conserve energy. Imagine how short-lived the battery would be if the screen was on during the time of an hour-long conversation. You can get the screen to turn back on by tapping the screen or simply covering and then uncovering (give it a second or so) the sensor. It's neat, because you can view your messages, text, view your contacts, and more as you are talking.

Lastly, the screen being off shouldn't make ending the call hard. Maybe I'm just old-fashioned, but I end my call with the soft key (the actual button) as opposed to the touch-screen.