Are you looking to change the original? Or are you looking to use Winterboard to change it
I don't remember the exact path for the 3G/4G/LTE icon, but if you want to theme it using Winterboard
Go to /var/stash/Themes.XXXXX/ and create a new directory. Name it whatever you want. For sample purposes, I'll call it LTE logo.theme.
So my new folder created is /var/stash/Themes.XXXXX/LTE logo.theme.
Now I'll create a subfolder inside and name it UIImages
Result: /var/stash/Themes.XXXXX/LTE logo.theme/UIImages
Now inside that folder, I'll put my LTE modded logo/icons for different formats.
The names MUST match the following:
You can incorporate the BlackEtch mods as well but you probably won't use it for the most part.
The size can be whatever you want within reason really. You can make it as long as what you had for Zeppelin on your carrier logo. But it shouldn't be any "taller" than the "height" of the statusBar or it'll look pretty weird. Implement it using Winterboard and respring.