Inkling is a popular virtual textbook publisher on the iPad, and it's recently expanded over to the web, allowing students to access their virtual textbooks from anywhere. Now, the company is adding one more platform to its repertoire: the iPhone. The Inkling app is now universal, which means you can browse, buy, and read textbooks from the iPad, the iPhone, or the iPod touch.
I don't know how much this will add to Inkling's business. You have to think that most students do their work on a computer or an iPad rather than on the iPhone's relatively small screen. But then again, I've done quite a bit of reading on my phone while out and about, and maybe there's an audience for academic texts in the same way. If you're an Inkling user, you can update the app and enjoy the new version right now.
Apple iPad Air 2
Apple iPhone 6s