So far i done this on both my ip4 4.1 and wife ip4 4.1 no problem lea.
Ok , i tried to provide more detail steps,
1) Jalbreak iphone with afc2add installed via cydia.
2) download ifunbox via
i-FunBox | File Manager, Browser, Explorer, Transfer Tool for iPhone, iPad & iPod Touch via USB
3) Run ifunbox with iphone connected via USB
4) navigate to phone>raw file system>var>mobile>library>carrier bundle.bundle
5) notice the 2 png file of your carrier without @2x filename.
6) You just need to drag and drop from your pc to ifun box directory the image file and rename it exactly the same but with @2x.png (example
FSO_CARRIER_M1-3GSM@2x.png) drag and drop the same image file to ifunbox and rename
Default_CARRIER_M1-3GSM@2x.png .
Turn on airplane and off back to see changes.
my carrier is m1 . If your carrier is starhub or singtel . Just follow the initial file name at the directory and add @2x .
There is no need to del away the 2 file with the name without @2x cause it will not affect at all.
Hope the above steps works for you guys.
PS. you can rename at ifunbox using right click on the file.