Iran's attempts to stifle dissenting views through online censorship don't usually work all that well, so it's trying a new strategy: bringing more of that data within its own borders. It's ordering messaging app developers to move all their Iranian users' data to the country within the next year if they want to "ensure their continued activity." It's not hard to see Iran would do this, of course -- in theory, this makes it easy to delete unwanted content, spy on traffic and seize servers.
The clamp-down is potentially rough for secure messaging services like Telegram, which are particularly popular thanks to encryption that keeps messages safe from the government's prying eyes. As Reuters points out, there are 20 million Iranian Telegram users in a country with just 80 million people -- it'd be a big blow if Telegram had to withdraw.
Whether or not companies like this actually have to withdraw is another matter. Iranians are used to circumventing bans through technologies like virtual private networks, so an attempt to block messaging apps might do little more than introduce an additional step into the connection process. Unless Iran finds a way to completely shut off outside access, this move could be more symbolic than it is practical.