The Data Consumption Vector
The iPhone includes a deeply integrated networking feature known as Wi-Fi Assist. By default, when your device is connected to a weak, stuttering, or incredibly slow Wi-Fi network (such as a public cafe hotspot or the very edge of your home router’s range), the operating system will silently abandon the Wi-Fi connection and seamlessly switch over to your cellular data connection to ensure webpages continue to load quickly. While this provides a smooth browsing experience, it can absolutely decimate a limited monthly data cap without any warning.
How to Disable Wi-Fi Assist
You can force your iPhone to stubbornly cling to your Wi-Fi connection, ensuring it never automatically consumes your cellular data allowance.
1. Open the Settings app on your iPhone.
2. Tap on Cellular (or Mobile Data, depending on your region).
3. This menu displays a massive list of every application that uses data. You must scroll all the way to the absolute bottom of this incredibly long list.
4. Right at the bottom, below the final app, you will find a toggle switch labelled Wi-Fi Assist.
5. Tap the toggle to switch it to the Off position (the switch will turn grey).
Your iPhone will now strictly obey your manual networking choices. If a Wi-Fi network becomes unusable, the phone will simply fail to load the webpage, rather than secretly consuming your cellular data to bridge the gap.