Earlier this year Nokia announced a special "protective case" version of the replaceable shell for the Lumia 620. The accessory, the CC-3061 protective shell, improves dust and splash protection, meeting the requirement for IP54 certification. The CC-3061 first became available in limited quantities in July, but is now more readily available. For example, it can be purchased through a number of retailers including Amazon UK (from £21), via eBay (around £23), and via Expansys (£16.99).
The CC-3061 is a replacement for a standard Nokia Lumia 620 shell and at first glance there's little difference between the two. However, the gaps between the display and the shell, as well as the side buttons and the shell, are better sealed. In addition the mesh that covers the loudspeaker in denser, making it harder for dust to get in.
The materials that the shells are made from are also different. The inner layer uses the standard polycarbonate (rigid), but the outer layer is made of TPSiV, a rubber like material, giving a softer (and bouncier finish). The TPSiV material wrap further round the front that standard Lumia 620 shells, which, together with its impact absorption properties, gives greater protection if the phone is dropped.
The CC-3061 remains something of a specialist accessory, but is a useful accessory upgrade for those that work in environments where the phone might come into contact with dust or water splashes (e.g. building site, running in the rain).
It's worth noting that a Lumia 620 Active Edition, which pairs a standard Lumia 620 with the CC-3061, is also available in some countries (e.g. Finland). This Active Edition is also being sold through some of Nokia's direct to enterprise channels.