If i know correctly by using my phone, the little button on the top, next to the mini sd card is used to lock the screen and buttons, just click that and it will shut it off, but the phone will still remain active. Just click it again and the phone will come one. Nice thing it will also help cut down your quick use of the battery.
I have the audiovox 6600 i amagine that it's the same on that as mine. when you press the little power button it turns off the machine but pressing any button, as happens quite frequintley in a pocket or on your hip, truns the thing back on. you have to go into the settings and look for button lock that will lock all buttons (expcept the power button) when the phone is off. The audiovox is also an always on system so phone calls will still come through when the device is off.