The Iranian government puts some considerable effort into monitoring Internet and other media outlets. But it also long ago decided that it's advantageous to the regime to allow intellectuals to say whatever they want in journals that nobody reads. Therefore, the Iranian regime concentrates on state-run television and other mass media, while leaving alone literary journals, obscure artistic presentations, and movies and so on.
We in the west may be impressed that there are these remarkable pro-human rights, pro-democracy articles written in Iran, but that's because nobody gets to read them. What everybody sees in Iran is the very rigidly controlled state-run television and the very widely available newspapers, and those are very tightly controlled.
The government has a problem with the Internet, and they're working very hard on that. But with modern technology advances, text messaging has become a popular way to spread news in Iran, and the government now has to figure out how to do something about that. The intelligence minister announced last week that he has to have a big new program to control text messaging, but so far it hasn't really come into effect.