Couldn't be simpler
I got a One NZ eSim with 40Gig of data for travelling in New Zealand especially for using Waze as SatNav in hire cars. eSim was dead easy to set up before leaving home then dialled 777 when we were waiting for our luggage at the airport in NZ and off we went. Great option for travelling as it would have cost me £6.60 per day to use data from my UK provider. WhatsApp works great for messages as normal.