Sad face. Right now, on my iPhone:
"iOS 9.3.5 provides an important security update for your iPhone"
40.5 MB. Great! Tapped "Download and install". It's greyed out. Huh?
Oh, "this important security update requires a Wi-Fi network connection to download". Really? It's only 40.5 MB. Let me decide, please, how I use my data.
Am I missing a setting that allows me to install an important security update on a network of my choosing?