When you don't have access to Wi-Fi, cellular data, also called mobile data in many countries, is your window to the internet.
However, you might see Could Not Activate Cellular Data Network as an alert. Other times, the top status bar may only show No Service or Searching. In all these situations, cellular data won't work.
If internet via 3G, 4G, LTE, or 5G is not working on your iPhone or cellular iPad, follow these solutions to fix the issue.