Telegram completed rolling out its free encrypted voice calls to users globally last week. But in a statement on April 17, the company said mobile operators and home internet providers had begun blocking the new feature the previous day, Bloomberg reported.
"We did not receive any communications regarding the reasons, so we have no idea what could stand behind the decision," Telegram said in the statement. "However, the fact that other voice over internet protocol providers in the country are still operating normally clearly suggests that this move is targeting Telegram specifically."
Mahmoud Vaezi, Iran’s Minister of Information and Telecommunications, told reporters that the block is a result of a judicial ruling issued to all phone operators, according to the semi-official Iranian Students’ News Agency.
Users in Iran can still use the service provided both ends use encrypted networks, Telegram added in the statement. Others applications such as Facebook Inc.’s WhatsApp and iMessager, and Microsoft Corp.’s Skype have voice call features enabled in the country. Whatsapp calls are generally not blocked in Iran, but this varies between phone operators. Twitter Inc. and Facebook, however, can only be accessed through VPNs.Telegram is a popular platform for citizens in Iran. The app, which is also used for file-sharing, originally became popular in part because of its emphasis on security, and its ability for users to conduct "secret chats" in which messages can be formatted to automatically delete themselves after being viewed.
"Telegram is providing a service that cannot as directly be surveilled as normal telephone calls," said Collin Anderson, an independent researcher focused on Iranian cyber policy.
However, Anderson added that there could be more "banal motivations" for Telegram’s voice feature being blocked. "These restrictions are often economically motivated – the applications cut into the revenue generated by charging for text messages and airtime," he said.
More than 20 million people in Iran use Telegram, which is about a quarter of the population, the Iranian Students Polling agency said in December 2015, citing a survey it conducted based on a sample of 4,390 people in provinces nationwide. About 48 percent of respondents in Tehran said they used the application, according to the poll.