As a post this contains nothing but a headline and a link. It is a bad post unless you're only interested in the link. There isn't even any relevant discussion or comment from OP.
There aren't, really. There are a few antiques and half baked things.
A big problem is that these days, unless you're the size of Apple or Samsung, it's impossible to get a reasonable hardware soc and modem other than one which only runs a soon obsolete blob laden android which is going to be EOL before you've even finished your design.
The hardware is not there. The firmware/hw data/platform isn't there even to begin OS work with. And there's a global shipping, regulation and mobile operator hell waiting on the other side. And a product lifecycle that's only a few years long.
Looks like an axe stone. Can't recommend a good tutorial other than a scout who knows. But you might find some. The key is a grip that keeps all your fingers on the rim and away from the side you're using.
Now if possible legal and contract things allow it get fixed and a number of employers start to offer this and pull in valuable workers... That might make the others nervous.
https://en.wikipedia.org/wiki/Reverend_Bizarre