Apple recently released iOS 9, implementing a new feature which is costing people with limited data plans hundreds of dollars. “Wi-Fi Assist,” which is on by default, will automatically switch you to 4G if it thinks the WiFi you’re using is too slow. If you’re on a limited data plan, that’s bad news and can lead to some astronomical cell phone bills.
To turn off this feature, simply, 1. Open your settings; 2. Choose “Cellular”; 3. Scroll all the way to the bottom to find “Wi-Fi Assist.” Finally, touch the button to turn it off. Voila!
Additional tip: Switching from Wi-Fi if on a company network also discounts shared drives and printers.