My latest column on the topic is here. Bottom line?
Mobile devices are following two contradictory trajectories. One class is fragmenting in terms of core functions, creating new markets for stand-alone devices such as dedicated cameras and media players. The other, which includes such devices as smartphones and mobile Internet devices, is taking on new features and functions, rivaling stand-alone devices in terms of functionality through convergence. Neither approach is universally correct, and vendors more than ever need to understand the contextual factors that influence consumer device usage. They have to focus on providing the sorts of core features that will lead users to include these devices among the three that they’re willing to carry. Devices that can’t displace one of those three will simply not be purchased.