If you care about changing your iOS version visually on your iPhone for some reason, then you can useFirmware Changer instead of editing .plist files and making a complicated process. Firmware Changerwill not let you update to iOS 4.1 but it will fake to be on iOS 4.1 or any other version.
You may want to change your firmware changer so that iTunes doesn't annoy you with the update message or may be to install some app that works only on iOS 4.1. Anyway, Firmware Changer is a free tweak available in Cydia via ModMyi repository. You need to have a jailbroken device to be able to use this app, follow our step by step guide posted here to jailbreak your iPhone or iPod touch usingLimera1n (may be GreenPois0n if you hate Geohot!)
