For many years, cellphone users who wanted to make sure they wouldn't lose their phones' address books in the case of a problem, or wanted to be able to easily transfer them to a new phone, would back up their contacts to their phone's SIM card. But on the iPhone, there isn't an obvious way to do this. So the question is: how do you backup contacts to the iPhone SIM card?
The answer is that you don't.
The iPhone doesn't store that kind of data on its SIM card because it doesn't need to. Earlier cellphones did this because there was no regular means of backing up data on them. The iPhone, however, makes a backup of its data every time you sync it to your computer (it can, of course, also back up that data to iCloud, too). This backup includes your address book entries, and many other things.
As a result, if you need to restore lost data, or transfer your data to a new phone, all you need to do is connect the phone to your computer that has your iPhone backups on it and then restore that data to your phone—or, if you use iCloud, restore from there.
That's much easier than trying to backup your contacts to your iPhone SIM.
If you're truly committed to moving contacts data to your SIM, there are apps that can do this if your iPhone is jailbroken. But remember that jailbreaking can be a tricky business and isn't recommended for users who don't have a lot of technical skill.
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