Apple has issued a Carrier Update
for Verizon iPhone 5 devices this evening to eliminate an issue where Verizon Cellular Data would be used while the iPhone 5 is connected to a Wi-Fi network.
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. Follow these instructions to install the update.
1. Tap Settings > General > About.
2. Wait for the following alert to appear: (top right)
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.
Note: To finish the installation of the update, your iPhone 5 must be turned off and then on again. After your iPhone restarts, tap Settings > General > About, then scroll down to Carrier and verify that "Verizon 13.1" is displayed.
The update has to be performed somewhat manually but is delivered over-the-air, per the instructions above. Apple describes the update as an "important new carrier update" but doesn't provide many details on how/when these circumstances might arise.