I remember how data plans on our for mobile numbers used to be a luxury, and that one had to enable it before being even allowed access to the Internet.
In short, no data plan, no Internet for you.
This is not the case nowadays where Internet access is available even if you didn’t subscribe to a data plan, which is rather dangerous for the not-so-literate when it comes to setting up mobile devices. You could unknowingly rack up a bill just for a mistake in the setting.
More often than not, this happens when someone inherits a device from another.
For a techie / geek / nerd / whatever bad names you call people like myself, we usually just do a factory reset. That’s all fine.
For those that are on the other side of the spectrum, they’ll just insert the SIM card and use it without checking other settings. We can’t blame them for their simplistic approach towards mobile devices, after all mobile phones were just phones that were mobile in a not-too-distant past but nowadays, it’s actually our mobile computer.
Almost every device these days have a setting that allows you to toggle mobile data use. In Android, it’s located in the Data Usage section.
Mobile Data should be off by default but if the previous user has it ON, it will be ON and data charges might be incurred.
I do not have an iPhone so there’s no screenshot from an iOS device but nevertheless, just seek your nearest Apple user (there should be plenty around) for assistance.
You have been warned.
My recommendation is that if someone wishes you to have their device, do request them to do a factory reset before the change of ownership.