This iPhone guide covers system and app-level ways to reduce cellular data use. It explains what Low Data Mode changes, how to review usage by app, and how to limit background refresh or disable cellular data for selected apps—along with the resulting trade-offs in media quality and automatic activity. Limit data usage on your iPhone Low Data Mode reduces data usage. You'll find it in Settings > Cellular > Data Mode. If you have more than one SIM, choose which one you...