My summary of the video is "You can set up a wifi network which a smartphone can be connected to by putting a SIM card into the phone, this does not require entering a wifi password or key on the smartphone but it does need a lot of hardware and software infrastructure setup work".

This video would be much better if the first minute was a better overview of what carrier-wifi is and what can be achieved by setting it up yourself.

Most of the video is about technical details.

Can you do anything slightly interesting such as creating SIM cards that let a smartphone act like you have your own telephone network capable of voice calls/SMS, but only over wifi?

I'v looked at the github page and still have no idea what this is capable of.