A study recently found that a quarter of mobile phones sold in Western Europe had been purchased online, mostly from Amazon (NSDQ: AMZN) and eBay (NSDQ: EBAY). The discovery led BusinessWeek to wonder how their role as major retailers could affect “the way carriers and device manufacturers market, subsidize and sell products and services, and how much revenue and profit they receive.” The study was conducted by TNS ComTech, which based results on the responses from 60,000 consumers.

The author argues that if eBay and Amazon continue to gain power—at least in some countries—they could launch handsets and services under their own brands (an evolution from Amazon’s Kindle e-book reader, which is already using Sprint’s network). But what the author didn’t bring up, and might be more realistic is that these outlets could become digital storefronts, as well, by providing a place where users buy digital content. Amazon is already doing this with its MP3 storefronts on the Android and Palm (NSDQ: PALM) Pre devices. If you buy your phone from them, why wouldn’t you return to buy music, books, games, newspaper subscriptions or applications? For eBay, the used market will likely shake-out different, but today it’s PayPal division is the payment platform for Research In Motion’s BlackBerry App World.