So, I'm running CM, and since I just did this for essentially myself, and didn't want to take the time incorporating this into the settings app, etc, I just modded the necessary framework files (from decompiled source, rather than original .java source, I come from HTC devices where source is not an option, and I'm a glutten for punishment), so that I could display custom text on BOTH the lockscreen as well as both notification panels.
Lockscreen versus notification are two different framework locations, so I just modded the frameworks to look for a text file in /system/ (lock.txt, notification.txt), the contents of each text file being the text you want to display in the corresponding locations (lock screen and notification panels).
Lockscreen (see bottom of screen):
Notification Panels (see bottom for screen 1, and the carrier text on tile for screen 2):
I have a heavily modified framework for personal "tweaks" so if anyone is interested in using this approach, I can package it up with some instructions, but it will take me a bit, as I would have to start over for modding from an original / unmodified framework to start.