TEHRAN � Rushing for a plane to Tehran because of a family emergency, the Iranian-American businessman stuffed his mobile phone into his carry-on, forgetting to turn it off.


It was useless in Iran anyway, he knew. American mobile phones never worked in the country, and even after the recent nuclear deal, many economic sanctions remain in place, frustrating foreign businesses interested in cracking the Iranian market.


So it was something of a shock when, having fallen asleep after arriving at his sick grandmother�s house in Tehran, the businessman, Faryar Ghazanfari, an intellectual-property lawyer, heard a buzzing coming from the bag.


At first, he thought it was an alarm. Then he picked up. �I couldn�t believe what was happening,� he said. �It was San Francisco. A colleague wanted an update on a patent case.�


Until recently, an American phone in Iran would not receive any signal. But that has quietly changed. This past week, a spokesman for AT&T acknowledged that the company was providing voice and data service in Iran to its customers with American phones through a partnership with a local firm, RighTel. An employee at the Iranian company, fully owned by a state entity, confirmed the partnership.


While the announcement that Airbus and Boeing will provide dozens of jetliners to Iranian carriers garnered worldwide headlines last month, the deal that AT&T clinched in March, making it the only American provider to offer phone service in Iran, flew under the radar.


The agreement is one of the few signs that the promises President Hassan Rouhani made long ago of welcoming Western businesses and ending Iran�s isolation are at last beginning to be realized.


�This is a step in the right direction,� Masoud Daneshmand, an official at the Iran Chamber of Commerce, said of AT&T�s partnership with RighTel. �The fact that phones are working in Iran and the United States is a sign of good will on both sides.�


With its oil wealth and nearly 80 million consumers, Iran has long held out the promise of a lucrative, if elusive, market for Western companies. In the immediate aftermath of the nuclear deal in January and the lifting of many economic sanctions, there were heightened expectations in both countries that the day had finally arrived.


But enough sanctions remained that Western banks refused to finance commerce with Iran without specific licenses from the United States Treasury. That seemed to choke off most business opportunities outside the oil and gas sector and the airlines. But for whatever reasons, AT&T decided to move ahead, apparently determined to shun publicity about its moves.


It remains unclear how AT&T and RighTel will settle accounts. A representative for AT&T said the company would not disclose information on financial arrangements made with the Treasury or with its Iranian partner. One possible clue: RighTel is owned by the Social Security Organization of Iran, a state entity that has large stakes in several domestic banks.


The Treasury would also not speak about the deal, saying in a statement that it �generally does not comment on specific licenses or engagement with private parties.�


Nevertheless, having working American mobile phones in Iran sends a powerful message that times are changing, albeit very slowly.


�Now we are, of course, hoping that the United States lifts all trade restrictions on Iran,� Mr. Daneshmand said. �In return, we will lift visa restrictions for Americans.�


In the past, Iranian interest in AT&T was of a different nature. In 2011, Iranian hackers targeted the carrier along with several other companies, dozens of banks and even a small dam in a suburb of New York, the Justice Department wrote in a complaint this year. Seven Iranian computer specialists who regularly worked for the Islamic Revolutionary Guards Corps were accused of carrying out the attacks.


AT&T still faces the many hurdles that all companies have in doing business in Iran. In addition to its endemic corruption and bureaucratic inefficiency, Iran works on a calendar different from the West�s, with different months and a Thursday-Friday weekend. The communication infrastructure is poor but improving, and many websites are blocked by the government.


And there is still the possibility of opposition from conservative clerics and Iran�s supreme leader, Ayatollah Ali Khamenei, who could end the arrangement in a flash if he felt it was inappropriate.


For Iranian hard-liners, direct service to the United States means yet another connection to the �Great Satan,� the place they wish death upon in every Friday Prayer. For many of them, simply the idea of an ever-friendlier and familiar America is a threat to the founding ideology of the Islamic republic.


For many, perhaps, but by no means all. �If we get service in return, it is not that bad,� said Mohammad Javad Helali, a Shiite Muslim cleric connected to the hard-line faction. �We just hope that the services will be free from infiltration by American intelligence services.�


The opening up of phone service is undoubtedly a welcome surprise to Iranians and the approximately two million Iranians living in the United States, many of whom travel frequently to their home country.


Azad Jafarian, an Iranian-American filmmaker, said his mother had just flown in from Los Angeles through a connection in the Persian Gulf state of Qatar, and he smiled when he saw her turning off the flight mode on her cellphone, bringing it back to normal operating status.


What happened next startled him. �I was driving her home, I saw her swiping her phone, and seconds later the phone started ringing,� Mr. Jafarian recalled. In a light panic, he told her to turn it off. �I was like, �This can�t be real.��


This article was written by� Thomas Erdbrink for The New York Times on Oct 08, 2016.