@Papaclifunfortunately roaming add-ons are only available for U.S. travel, so you won;t be able to use your PM service while in Costa Rica. If you'll be there for awhile (i.e. more than 3 days), I suggest getting your phone unlocked (if you haven't done so already), and just get a local SIM while you're down there. You can easily get one set up before you leave their airport, there's always cell service companies located inside or just outside the airport.
If you don;t want to spend the extra money, then you can use app services like WhatsApp on your Wifi, but then again there's gonna be quite a bit of hassle looking for a wifi signal, let alone an open signal, unless you pkan on only using at your hotel. Also keep in mind the hotel Wifi might not be free either. Gotta remember you're not going to Hong Kong, so wifi signal might not be as readily available as you'd think.
