Cuba has long been one of the least digitally connected countries in the world, but that is slowly changing. The island country recently opened up 35 public WiFi access points nationwide.
Mobile service in Cuba is provided by state carrier Cubacel, which sells SIM cards at their offices in Havana and at its Jose Marti International Airport. International calls are expensive.
Internet in Cuba is expensive and slow, and only a small percentage of the population enjoys regular internet access. Some options are available to visitors, but don't expect easy or fast connectivity.