After schooling the publishing industry on how interactive ebooks could be tackled on the iPad, Inkling is now focusing on the iPhone’s much smaller screen with its latest release.

Inkling 3.0 brings the company’s extensive library of digital textbooks, cookbooks, and Frommer’s travel guides to the iPhone and iPod Touch. The news comes a few months after Inkling opened up its platform to the Web, allowing anyone with a web browser to access its titles.

While the iPhone’s 3.5-inch screen isn’t exactly conducive to long reading sessions, the new app means that Inkling is primed for the release of the iPhone 5 (or whatever it’ll be called), which is expected to have a 4-inch display. The company says that more than 4,000 schools are using its platform for digital textbooks, so the addition of iPhone support will also give students less of an excuse for not doing their class reading.

The iPhone app contains all of the features of its iPad sibling, including real-time synchronization for highlights and bookmarks, reading assessments, and an interface optimized for the smaller display. The iPhone Inkling app also lets you download individual chapters from books, so you don’t have to waste space storing an entire title.

Now that Inkling has conquered the Web and all iOS devices, the company needs to target Android. It made sense for Inkling to avoid Android tablets so far, given their overall poor showing in quality and sales. But with the success of the Nexus 7, which is both cheap and powerful, Inkling won’t be able to ignore Android for much longer.

San Francisco, Calif-based Inkling was founded in 2009 and raised a round of $17 million last summer from Tenaya Capital, Jafco Ventures, Pearson Education, and Sequoia Capital.