• by Joe Mandese  @mp_joemandese, August 21, 2012

Just sitting here scanning my inbound and surfing the Web for breaking news as I get ready for Day Two of the Mobile Insider Summit in Lake Tahoe (could be worse places to scan and surf, right?), and lo and behold another relevant story pitch comes through, this time from the researchers at NPD Group, who are clearly on the case of mobile consumers. And it seems the mobile accessory that is most important to them is, in fact, the case. And they’re paying for it.

Revenues from mobile phone accessories in the U.S. jumped 32% during the first half of 2012, making it by far the highest growth accessory category. That makes sense, because they’re also the most popular, growing 69% over the past year, followed by stereo headphones with microphones, which grew 67% year-over-year.

Cases are also an improving margin item for retailers – online and off – with average prices rising 25% in the past year.

The findings, which come from NPD’s just-released “Mobile Phone Accessories Attach Rate Study” (okay so they’re better at conducting research than naming reports, but that’s what snarky trade reporters are for, right?), also generated an insight that is worthy of further investigation – maybe even a case of its own: And that is where consumers are buying their mobile accessories – in-store, or online?

Given all the attention to showrooming – a subject that is also on a panel at the Mobile Insider Summit later today – I can just envision mobile consumers wandering around a store just after purchasing their new phone, eyeballing the sleek accessories on the retailer’s shelves, and then using said device to surf the mobile Web for better options, or maybe even just better prices.

So far, that doesn’t seem to be the, er, case.

According to NPD, nearly half of all consumers who bought their phones in-store also bought their accessory at the time of purchase.

“In-store buyers also tended to spend more on add-ons at the time of their purchases, spending nearly three times as much as those who acquired their phones in online or over-the-phone channels,” the NPD report finds.

That said, NPD noted that mobile phone retailers are “missing out” on a significant amount of post-purchase accessory upselling after consumers leave their store, or website: “Among those mobile phone buyers who bought accessories within the first six months after the original phone transaction, four out of five reported visiting a different retailer from their mobile phone seller to make these aftermarket accessory purchases.”

Case closed.