Customizing the iOS 7 status bar is only a tweak away with StatusModifier. Those with jailbroken iPhones can install this free tweak for more control over exactly what information is displayed. Hiding items or displaying the amount of free system RAM can be accomplished using Settings -> StatusModifier.
Custom formatting can be created using the DateFormat Builder, which provides options such as displaying seconds with the current time, or the date. This is also where iOS available RAM can be selected by entering the letters FM (free memory). By default, the amount of free memory is updated in real time every second, with a slider making longer intervals possible.
In addition to the DateFormat Builder, individual status bar items can be displayed or hidden. For example, simple toggles will turn off the Carrier name, rotation lock icon, or signal bar. Here is the complete list of items that can be hidden:
Wi-Fi / 3G
StatusModifier can be found on Cydia in the ModMyi repo for free. Look here for instructions on how to jailbreak iOS 7.x with evasi0n 7. You can also find out how to purchase and install Cydia tweaks with this guide.