A Maryland company called Washington Software, Inc., won the contract to distribute the text messages for Radio and TV Martí. Included in the company's marching orders: The firm must develop a system that will trick Cuban government censors so that all the text messages get through to cell phone users, no matter how sensitive the messages are.
Initially, the company must be able to send 24,000 messages per week. That amount could increase, depending on conditions and events in Cuba.
The messages would evidently go to subscribers, not random cell phone users, so I wouldn't characterize this as text-message spam. Read more at the Cuba Money Project.
P.S. Ernesto Hernandez Busto at Penultimos Dias kindly points out that another text-messaging service exists: Cuba Sin Censura, which sends news headlines to cell phone users for free.