Whatsapp is the best. We’re split between 4 different countries and I have seriously saved thousands of $$$ the past 3.5 years. If you were trying to make reservations with a restaurant, either the restaurant or the manager would have to have the app on a cellular phone and you’d have to be contacts to communicate. Plus they would need to check their messages often for it to be effective.
I think it’s a wonderful tool and it saves everyone time and money. 👍
If I ever really needed to use my carrier service, I activated it, paid about US $10 per 24 hours. (Although in my currency it translates to about $30). In my experience, wifi on the island is very weak and unreliable. But I’ve rarely needed it if wifi wasn’t available.