This carrier settings update resolves an issue in which, under certain circumstances, iPhone 5 may use Verizon cellular data while the phone is connected to a Wi-Fi network.
To install the update:
1. Tap Settings > General > About.
2. Wait for the following alert to appear:
3. Tap OK to install the update.
4. Hold the Sleep/Wake button down until you see “slide to power off”.
5. Slide to power off.
6. After the device powers off, hold the Sleep/Wake button to turn your phone back on.
After your iPhone restarts, tap Settings > General > About, then scroll down to Carrier and verify that “Verizon 13.1″ is displayed.
More info via Apple.com here.