There is an option in sbsettings-more-sbs options-statusbar date but that will only give you the date in the status bar not the day of the week. I've had it enabled ever since I could jailbreak my ip4 sometimes I need to know the date when in a call, backing out to go to the calendar is a pain and a waste of time and if you try to go to the lock screen to see the date you will end the call. It's the small things like this that make jailbreaking great