Outside their native Japan, emoji have been available to in-the-know smartphone owners for some time via add-on applications. But now they may be on the verge of going mainstream in the United States, thanks in part to Apple’s latest update to its iPhone software. The latest version, iOS 5, comes with an installed library of emoji that can be turned on as an “international keyboard” in the device’s settings.

Apple declined to comment on its decision to add emoji, but it was most likely driven by a global standardization of the format last year that was meant to ensure that a picture of a cute cat will still look like a cute cat on a different phone in a different country. The move has put emoji on the radar of many more iPhone and iPod Touch owners.

Shawn Roberts, 39, a lawyer in Oklahoma City who was familiar with using emoji in e-mail services like Gmail, said they were an entertaining way to communicate with his 9-year-old son, Sam. Mr. Roberts said he and Sam often use pictures of tiny footballs or basketballs as they trade banter about sports and coming games.

“It’s just fun,” he said. “And it lets you convey a little more emotion or feeling in messages.”

Emoji have long been popular among cellphone users in Asia. They first emerged in Japan in the 1990s, said Mimi Ito, a cultural anthropologist at the University of California, Irvine, who studies how young people use digital media in Japan and the United States. Cellphone carriers first added the images to differentiate their phones from those of rivals, and they caught on as an efficient way to quickly convey a specific thought, mood or joke.