As you often see (especially on my iPhone as well as that of K-Rim), it is possible to change the name of Carrier on your iPhone without jailbreaking it.
So here is a tutorial explaining how to do it.
Plug in your device. Then, in iTunes, right click on your device -> Save.
Then launch the previously downloaded software, right click on the backup of your device and open.
Go to /Library/Preferences/com.apple.springboard.plist
Open the file “com.apple.springboard” and do ctrl + f
Search for “SBFakeCarrier”. Replace the element placed between the ”
Save and close the file.
If you can’t find SBFakeCarrier, add yourself:
Synchronize your device then restart it.
Final result :
Info. If that still hasn’t changed your CARRIER, restore your device from a backup;)