I would like to create a wifi network which does not have access to the Internet - that should not be a problem as there are plenty of posts already on Stack Exchange covering this topic.
However, what I didn't find on Stack Exchange is how to perform a "switch" - so that the local network gets shutdown and the pi uses a plugged in mobile antenna with a sim card in it to get access to the internet and send data.
Is that even possible? If so, how can I achieve something like that?
Any help would be appreciated :)