By default, the iPhone doesn't enable security measures that would prevent someone else from using it, should it be lost or stolen—or even temporarily "borrowed" without your knowledge. However, you can enable optional security features, primarily Passcode Lock and SIM PIN lock.
In this section, I first help you set up a passcode lock and a SIM PIN lock, and I discuss how to Handle Other Passwords (p. 160) for services like secure Web pages, email accounts, and voicemail.
Finally, I discuss how to Use a VPN (virtual private network) (p. 162), which you may wish to use when you access the Internet from a public hotspot or other remote location.
You can keep others from using your iPhone through two ...