Formatting is stored in:
/System/Library/Frameworks/AddressBookUI.framework/ABPhoneFormats.plist Download this file from your phone. The file is stored in binary format, so you'll need to convert it to text. Now save this file and open it in a text editor. Change the formatting under us to look like you want (if you find your region in the file, just copy from your region to the us). There's probably some way to just make it use your langauge (instead of 'us'), but i don't know where you specify that. When you are done changing formatting, save the file and upload it to the iPhone in same directory you found it. You don't need to convert i back to binary.