Mobile phones in Tehran started beeping and buzzing well before Iran's nuclear agreement with the West was finalized. They carried an important sentiment that couldn't wait for the niggling details to be ironed out in the talks between Iran, on one side, and China, France, Germany, Russia, the U.K., and the U.S. on the other.

"Congratulations, the agreement is almost signed! Come dine with us for less," read the text from a local pizzeria. Discounts and specials celebrating the coming end of the sanctions pinged around the capital.

In the offices of Takhfifan, Iran's answer to Groupon, staffers interrupted their weekly meeting every 10 minutes to refresh the news on their laptops. "We're all counting the seconds," said Nazanin Daneshvar, the site's founder, hoping "that we'll get back to a better place after such a long, difficult time." Daneshvar's marketing platform is thriving: It boasts a million subscribers who grab daily deals on everything from concert tickets to swimming pool passes. An Iran reopened for global business could eventually bring in Western companies and investors, which might finally mean economic growth of a different scale. A normal scale.

Even normality—the most modest expectation—would be vastly different from the Tehran I last experienced in 2009, before that summer's Green Movement uprising. Like many dual-national Iranian journalists, I haven't dared to return since the violent suppression of the protests. (Reporter Jason Rezaian of the Washington Post has been detained on espionage charges for more than a year.) I've followed the country through family and friends, most of whom tell the same tale: six years of diminished hopes and sullenness, brought on by global economic ostracism.

The nuclear deal changes everything. The West—and most Americans—view a rapprochement with the Islamic Republic with uncertainty and some dread, but in Iran there's a thirst for reengagement. Ordinary Iranians and even some businesspeople predict the relief from sanctions will be quick and visceral. "There's simply a huge amount of key technology we either don't have access to or have to pay twice as much for under the table," says a prominent petrochemical industry figure, who asked not to be named because of security concerns. He says the cash-strapped government has been paying engineering companies with shiploads of oil. "It will be a relief simply getting paid with regular cash."