PhoneThe country code for Cuba is 53. GSM cell phones will work in Cuba.
Cellphones can be rented at several stores in Havana, including one in the airport. The rates are CUC9 per day (CUC6 for the phone and CUC3 for the SIM card), plus about 36 cents a minute for prepaid cards. If you bring an unlocked GSM phone operating at 900 MHz (or quad-band world phone) you can buy a SIM card for CUC111, plus your prepaid minutes.
LanguageThe official language of Cuba is Spanish and the vast majority of Cubans speak it. Lucumi, a dialect of the West African language Yoruba, is also used as a liturgical language by practitioners of Santería, and so only as a second language. Haitian Creole is the second largest language in Cuba, and is spoken by Haitian immigrants and their descendants. Other languages spoken by immigrants include Galician and Corsican.
Basic to fair English is spoken in some tourist locations and language should not be a deterrent to visiting the country for non-Spanish speaking tourists capable of speaking English, though basic Spanish would prove useful, especially in more informal settings. Cubans enjoy talking to tourists, especially if you are staying with them in the "Casas particulares" and some knowledge of Spanish will help you understand regular Cubans' experiences. Cubans tend to swallow the last syllable in a word and generally swallow the 's' sound.
InternetIn many cities the only way for tourists to access the internet is through the government's communications centers. This is payable by purchasing a prepaid scratch card with a PIN code granting you access for one hour. The same card can be used throughout the country at any ETECSA terminal, allowing you to disconnect after your session and use the remaining time on the card further at the next hotel/city you go to.
Wi-Fi in hotels and restaurants is certainly uncommon if not non-existent and tourists should not rely on this being available when planning their means of communication.