So i had a reg. iphone 3G and it was jailbroken and such and i changed the AT&T logo to a japaense letter. and now on my 3G S it still shows it but this phone is NOT jailbroken how can i fix this?!
you will have to jailbreak it to change it back. Right now that carrier name is locked in. The only way to gain access to it is by accessing the firmware and modifying it...that's jailbreaking.
All you had to do was set your new iPhone as new. The carrier logo is a setting that gets backed-up so when you restore from back-up anything that set as logo name before gets transfered.