How di I get my K850i to show the time in screen...

Question

My previous Sony Ericsson Cybershot showed the time on the screen when it went into sleep mode. It also showed an envelope next to the time in sleep mode. At the moment, after 1 minute my screen just goes black, as if it is switched off. I then need to press any button to check to see if I have any message. It was a really helpful feature but I can't get my new K850i to do this. Help!