The surprise first phone contact Friday between presidents Barack Obama and Hassan Rouhani was not only a dramatic moment in US-Iranian ties, but also in the field of digital diplomacy.
US President Barack Obama speaks to members of the press in the briefing room of the White House September 27, 2013 in Washington, DC about a phone conversation he had with Iranian President Hassan Rouhani and a looming government shutdown.
Moments before the US leader announced from the White House podium that he had a chat with his opposite number, the Iranian president had sent a tweet that could live in history.
"In a phone conversation b/w #Iranian & #US Presidents just now: @HassanRouhani: 'Have a Nice Day!' @BarackObama: 'Thank you. Khodahafez,'" it read.
Rouhani's account appeared on Twitter after his election this year and his English-language messages have become a symbol of Tehran's diplomatic outreach.
There has been some controversy about the account at home. It has not been officially confirmed as his and social networking sites are banned to ordinary citizens.
But throughout his visit this week to the UN General Assembly in New York, Rouhani's office has used the stream to keep followers up to date with his speeches and media appearances.
Any lingering doubts that the account is run by his office evaporated when it confirmed the phone call before the White House did.
And on Friday, even as Obama spoke in the more traditional venue of the White House briefing room, Rouhani outlined his side of the exchange online.
"President #Rouhani and President @BarackObama expressed their mutual political #will to rapidly solve the #nuclear issue," he said.
"Obama, @HassanRouhani appoint Foreign Ministers to follow up cooperation ASAP.
"@BarackObama to @HassanRouhani: I express my respect for you and ppl of #Iran. I'm convinced that relations between Iran and US..1/3
"@HassanRouhani to @BarackObama: We're hopeful about what we will see from P5+1 and your govt in particular in coming weeks and months..2/3
"@HassanRouhani to @BarackObama: I express my gratitude for your #hospitality and your phone call. Have a good day Mr President. 3/3
"@BarackObama to @HassanRouhani: Thank you, Khodahafez."
The tweets raced around the world and, stunning many observers -- not all of them disinterested figures -- who sensed that history was being made.
"I feel like I'm witnessing a tectonic shift in the geo-political landscape reading @HassanRouhani tweets. Fascinating," tweeted Twitter CEO Dick Costolo.
Costolo doubtless has his reasons to celebrate his own platform's role in the incident -- but there was a sign that he might have a point: Rouhani re-tweeted him.