You can now purchase pre paid calling chips for your mobile phones when you arrive at the airport. Look out for Kolbi signs. All you will need to get a local cell number is a jail broken phone, your passport, $5 and about half an hour of your time.
By the way, US appliances work in CR so no need for an adaptor.
FROM SAN JOSE AIRPORT
+506 2656 1150
or toll free from USA/Canada 1888 575 6247