score:3
There are public phones in Cuba, and they look like this
In order to call you need phone card (tarjeta propia) sold at ETECSA stores, it has blue color. Phone cards are sold in CUCs ($5, $10, and $20) and in Cuban national currency (3, 5, and 7 pesos).
Addresses of ETECSA stores are listed here.
UPDATE: there are three types of phones in Cuba though:
Another, more expensive way, is making call from hotel landline, either from room or lobby.
But, all in all, I recommend you to apply some international roaming plan just in your home country and that's it. It would be much simpler and cheaper in majority of cases (it depends).