I really want an app for my iPhone. Amazon, Kobo, BN, Borders, iBooks and others have apps so I think it's important for Sony to remain competitive in this area. It is frustrating that they have expected people to use their Sony Reader Library software to buy their books rather than an interactive website.
To answer your question, yes, they have announced plans for smartphone apps but no specific dates. It was included in their press release in September when they announced the new 350/650/950 ereaders. You can find the entire press release at this link.
"In addition to the new devices in the US, Sony announced development of a set of applications for iPhone and the Android Marketplace to extend the Reader experience across multiple portable devices."
"With Reader™ Desktop Edition (formerly Reader Library) for Apple’s Mac OS X and Microsoft® Windows® and Reader™ Mobile Edition for Apple iPhone and Google Android-based smartphones, users will be able to synchronize their reading among multiple devices. These free applications, available later this year, will offer an intuitive digital reading experience with an elegant interface and access to Sony’s Reader Store for browsing and purchasing content."