Steve Ballmer, chief executive officer of Microsoft Corp., speaks at an event in San Francisco, California, U.S., on Monday, July, 16, 2012. (David Paul Morris/BLOOMBERG)

A surprise popped up in the iTunes Store on Friday: an iPhone version of Microsoft Office.

The app has its limitations. It’s free to download but works only for those who subscribe to Microsoft’s Office 365 service, which costs $10 a month or $100 a year. It’s not for the iPad, though it would benefit from the tablet’s larger screen that would make it easier to work with documents. And it works only with the suite’s three core programs: Word, Excel and PowerPoint.

But it is Office. And it’s on the iPhone.

With the app, users can edit documents started on other screens from Word, Excel and PowerPoint, making it easier to incorporate last-minute changes and suggestions into shared meeting materials that everyone on a team can see. Users can also create Word and Excel files from their phones, convenient for when you want to get a thought or figure down but don’t have a computer handy.

Because the app works with Office 365’s cloud capabilities, the changes that users make on their phones will show up across other devices. So the next time the user calls up the document on a laptop or desktop, it should reflect all the tweaks that were made on the go.

The app comes after long speculation over whether Microsoft would allow its essential software suite on smartphones from competitors. Office is one of Microsoft’s most important and iconic products and has been a major selling point for Microsoft’s Windows Phones and tablets running Windows RT and Windows 8.

But adding iOS support gives Microsoft the opportunity to reach a much wider audience in the smartphone market and sell more of the subscriptions it’s pushing for the wider Office suite.

For Apple consumers, the new app should be a welcome option. Most of the Office alternatives that have popped up to fill a demand for productivity software on the iPhone are, by and large, not as stable, as feature-rich or as easy to share with others.

That’s not to say that there isn’t some competition. Google, which has challenged Office with its flexible, portable Google Docs suite, has a Drive app that lets users make new word-processing documents or spreadsheets from the iPhone. Users can also upload photos or videos using the app and can edit a wider range of Drive documents.

And then there’s Apple itself. The iPhone maker announced earlier this week that it’s adapting its iWork suite for iCloud to make its product more competitive with Office 365. The software additions will enable Apple users to work with Pages, Numbers and Keynote files on the Web. Those files will also be Microsoft Office-compatible, the company said.

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