Actually the problem does have a solution -- it's just changed. The information for the carrier is now read from the Springboard.strings
file, located at
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator60.sdk/System/Library/CoreServices/SpringBoard.app/English.lproj/SpringBoard.strings
Note the simulator version part of this path will differ according to the version of XCode you are using -- I'm using 4.5. Note also that the default configuration for this file is binary but you can convert to XCode-editable-form with
plutil -convert xml1 Springboard.strings
Once you've done that, edit and change the value for the key SIMULATOR_CARRIER_STRING to what you want to use. You can use this same technique for non-EN languages--just edit the appropriate .../<lang.lproj>/Springboard.strings
file.