Pro-reformist supporters used mobile phones to spread their message
Reports from Iran say that SMS text messaging services have been unblocked for the first time since disputed presidential elections.
However, Iranian news agencies say there are still technical problems.
Text messaging and social networks were widely used by protesters in mass rallies following the election.
Defeated opposition candidate Mir Hossein Mousavi this week called on the government to end its interference in phone networks and the internet.
Correspondents say texting has been restricted since 11 June - the day before disputed elections which saw the controversial re-election of President Mahmoud Ahmadinejad.
The lifting of the restrictions has been reported by a number of Iranian news agencies monitored by the BBC, including Tabnak.ir, a conservative website believed to be associated with former Islamic Revolutionary Guards commander Mohsen Rezai.
Tabnak said that SMS services, although restored, were still blighted by technical problems.
Messages up to three weeks old were being sent out, and some users were receiving multiple repeated messages, it said.
The agency added that it had been unable to get an explanation for the problems from the communications authorities.
The conservative Hamshahri newspaper recently supported the cutting off of SMS across Iran, saying the measure had created tranquillity.
Mr Mousavi has denounced "illegal" interference by the government
However, parliamentary deputy Mostafa Kavakabian told the Farda News website that the blocking of SMS services had caused great damage to Iran's economy. He asked the Iranian parliament to investigate.
On Wednesday, Mr Mousavi published a statement on the internet in which he demanded an end to what he called the government's illegal interference in phone and SMS networks and the world wide web.
Tehran imposed severe restrictions on foreign media inside Iran when mass protests broke out following the election result.
Despite the restrictions, Mr Mousavi's supporters managed to get information and images of the protests to the wider world using mobile phones and social networking sites such as Facebook, Twitter and YouTube.
At one point the US state department asked Twitter to postpone planned maintenance work so that Iranians could communicate with each other.