66 percent of revenues earned from mobile phone handset accessories are generated in the aftermarket with items such as protective cases and memory cards.

According to a recent "Mobile Phone Accessories" study from ABI Research this percentage is expected to grow with time, following a market trend to move more and more accessories "out of the box" and onto retailers' shelves.

"Mobile operators and mobile phone vendors see that the only return from including a subsidized accessory included in the handset box is customer satisfaction," comments industry analyst Michael Morgan.

"While that isn't without some intangible value, on the retail shelf an accessory is a high-margin product that will generate actual income."

Because of that, aftermarket accessories will also show faster growth rates than those included "in-box."

The currently most popular aftermarket accessories are memory cards and protective silicone carrying-cases or sleeves. Both result from the popularity of smartphones: their multimedia capabilities often demand extra memory capacity, and their high value encourages owners to take better care of them.

This latter trend has clearly been initiated and driven by the Apple iPhone.

Protection takes on even greater importance in some emerging markets, where most owners intend to resell their phones when they upgrade.

Other regional factors in the accessories market are culturally determined, says Morgan: "While the belt-clip style of handset ‘holster', for example, is popular in North American and Western European markets, Asian consumers tend to prefer wrist- and neck-straps which provide greater visibility for the phones of the fashion-conscious, at lower cost."

Fast-growing accessory groups include Bluetooth headsets and wired headsets for music listening, while others such as add-on GPS receivers are in decline as their functions are progressively moved into the handset itself.