Nokia's plans for their handset future have leaked, courtesy of a house-shaped diagram that showed up in the mobile-review forums. The document, which appears to be part of an internal presentation, details everything from the basic entry-level Cseries and Eseries models, through midrange Cseries, Eseries and Xseries phones, up to the flagship N8 and hitherto-unconfirmed Nokia N9, with an Sseries "chimney" too.
Going by the French-language table alongside the diagram, the Sseries is reserved for devices Nokia don't believe slot into their regular N/E/X/C ranges. No suggestions as to what that might include at this stage. As for other unconfirmed phones, beyond the N9 there's also the E7, C7 and X7, together with the news that there won't - at least in the immediate future - be entry level Eseries devices below the E5, nor an X1.
Of course, Nokia's naming scheme is already pretty well understood, and with the N8 being official it doesn't seem too great a stretch for the N9; previous rumors have suggested that might have a physical QWERTY keyboard, though so far that's unconfirmed. However, we'll be keenly watching to see whatever evidence of the new Sseries might show up.