Apple has today released an update for Verizon's iPhone 5 to stop the devices from using Verizon's cellular network when connected to a Wi-Fi hotspot. Users had been reporting that their devices were using data, resulting in higher bills, even though they had been connected to Wi-Fi. The update has to be installed manually and Apple has provided the steps below. It's not yet known if to reimburse customers who had data charges due to the bug.
This carrier settings update resolves an issue in which, under certain circumstances, iPhone 5 may use Verizon cellular while the phone is connected to a Wi-Fi network. Follow these instructions to install the update.
Note: To finish the installation of the update, your iPhone 5 must be turned off and then on again.
New version 13.1 for Verizon under Settings/General/About the scroll to carrier
This was released a few days ago if I'm not mistaken...some have posted threads saying they had issues with the carrier update. I haven't...but then again, I wasn't having (or noticing) the data usage issues to begin with.