Recently acclaimed Cuban blogger Yoani Sanchez published this to her twitter page :
#twitter debe aclarar si su servicio nos ha censurado publicacion de tweets por sms o si ha sido el gobierno de#cuba que nos ha bloqueado
23 minutes ago via web
Translation: Twitter should clarify if they've censored the publishing of our tweets through SMS or if the Cuban government has blocked us
#cuba Bloquearon la publicacion desde moviles cubanos a twitter. Parece que pusieron el filtro aqui dentro.1 amigo publica por mi este tweet
about 3 hours ago via web
Translation: Cuba blocked the publication of twitter messages from Cuban mobile phones. It looks like they've put a filter. A friend is publishing this tweet for me.
There has been no confirmation as to whether she is correct and the government is blocking the signals or if it is a technical problem with twitter and/or Cuban cellphone service. Should it be true this would be a serious blow to many Cubans who use this technology as a vital lifeline to the world. Check back here for more info on the story as information comes in.