Q: I’ve recently upgraded to an iPhone 4 and am looking to convert my old iPhone 3G profile for my wife’s use. We both use the same iTunes library and account, so I’m wondering if there’s anything I need to do like reformat it or if I can simply change the profile to say her name instead of mine? The other issue is that it will want to update to the latest OS and I’m not sure how to prevent it from doing that, as I know that it’s not compatible with the newer versions.

– Ken
A: Since you’re using the same iTunes library and iTunes Store accounts, there may not be any reason that you need to worry about erasing and restoring the iPhone, although it certainly doesn’t hurt to do so if you wanted to start with a “clean” configuration rather than having to manually remove any apps or media content that your wife wouldn’t want or need.
That said, any inherent association of an iPhone or other iOS device is to an iTunes library, rather than a specific person. Obviously, information such as e-mail accounts will generally be configured for a specific user, but this is simply a matter of removing and/or reconfiguring these accounts and has nothing to do with how the device was originally setup or associated to a user.
If all you want to do is simply to change the name of the device to indicate that it’s your wife’s iPhone now, you can do this very easily in iTunes simply by connecting the iPhone to your computer and double-clicking it in the Devices list at the left-hand side of your iTunes window; the field will become editable and you can type in any name you want to rename the iPhone.
Note that this will only rename the iPhone without changing any of the other configuration or sync settings on the device. Once you’ve done this, you may still want to perform additional tasks such as changing the configured e-mail account, and adding or removing applications, music and video. Being an iPhone 3G, you won’t need to worry about things like reconfiguring an iCloud account, but for newer devices this is something you would likely want to check as well.
Alternatively, if you want to start with a clean slate and reconfigure the iPhone 3G from scratch, you can simply plug it into your computer and choose the “Restore” button from its Summary screen in iTunes.
This will erase everything on the iPhone 3G, returning it back to its original factory settings. Once the iPhone restarts, you will be asked whether you want to restore your old backup from iTunes or set it up as a new device; choosing to set it up as a new device will allow you to give it a new name and configure all of your settings and load apps and media content from scratch. The disadvantage to this method is that it is more time consuming, and if you already had apps on your iPhone 3G with data that you wanted to leave in place for your wife, there’s really no way to get this information back; all apps that you install will also begin with a clean slate.
Lastly, regarding the iOS version, you don’t need to worry about preventing the iPhone 3G from being upgraded to an incompatible version. Each individual hardware model has its own unique iOS package specific to that hardware; since iOS 4.2.1 was the last version ever created for the iPhone 3G, there simply are no newer versions available, so iTunes will simply report that there are no updates available for your old iPhone 3G. Newer iOS versions are only available for newer devices, and iTunes wouldn’t attempt to download an iPhone 4 package and install it on your iPhone 3G as that obviously wouldn’t work anyway, regardless of its version.