Nokia's smartphone, the Lumia 820, equipped with Microsoft Windows Phone 8, is displayed in New York.(Photo: Mark Lennihan, AP)Nokia has just done something pretty unusual: it's invited its users to effectively tailor an element of its smartphone hardware to their individual needs.As a Friday present for its more enterprising fans, the Finnish firm announced the release of what it calls a '3D-printing Development Kit', or 3DK, for the back shell of its Lumia 820 handset. Here's how Nokia community and developer marketing manager John Kneeland described it:"Our Lumia 820 has a removable shell that users can replace with Nokia-made shells in different colors, special ruggedized shells with extra shock and dust protection, and shells that add wireless charging capabilities found in the high-end Lumia 920 to the mid-range 820."Those are fantastic cases, and a great option for the vast majority of Nokia's Lumia 820 customers. But in addition to that, we are going to release 3D templates, case specs, recommended materials and best practices — everything someone versed in 3D printing needs to print their own custom Lumia 820 case."This makes Nokia unique among major handset manufacturers, at least so far. Yes, there are many 3D-printing schematics out there for iPhone cases, for example, that use Apple's official specifications. However, they are not part of the iPhone.Embracing inevitabilityWhat Nokia has done here is to invite a certain type of user to build a component of its product. In doing so, the company is hewing to its historical course of openness – you know, the one it was so keen on before the Microsoft partnership, when it tried to accelerate development of the Symbian platform by open-sourcing it. That was all about software, and Nokia messed up by not being timely in its code releases.This is about hardware, and Nokia can…