Richard Hayler has written an excellent tutorial on using this new add-on board from Pimoroni. You basically connect to the pHAT using minicom and then send old-style AT commands like you would with an old modem. He hasn’t quite gone so far as to show how it might be used practically as an IoT device, but I suspect that’s not far off. Read it here. To get hold of the pHAT, you can go to Pimoroni or The Pi Hut.
why would I use this?
Good question. I guess it’s good if you want to send short messages over wi-fi. It’s no use as a full-fledged internet connection, but for IoT messages I guess it would have some use.