The proportion of online retailers with mobile-tailored sites has tripled in the last year but still remains small, according to a new study. In its second annual mobile commerce audit, digital strategy firm Acquity Group found that 12% of the top 500 Internet retailers had sites optimized for mobile phones, up from 4% a year ago.

And despite all the buzz around mobile apps, the share of companies with downloadable mobile apps is only 7%, up from 2% last year. Only 5% had both a mobilized site and an app and only 2% had an e-commerce-enabled app. In terms of specific devices, 11% had apps for the iPhone -- up from 1% last year -- but few had ones geared to other smartphone platforms such as Android, Palm or the BlackBerry.

Only 12% of retailers had mobile sites that allowed customers to complete a transaction through checkout on at least one type of smartphone, and only 2% offered apps with check-out capability.

Tom Nawara, Acquity's head of digital strategy and design, said the weakened economy last year had slowed retailers' expansion into mobile, but that companies were refocusing attention on the emerging sector this year as business conditions have begun to improve. "We're hearing from clients now who are fairly mature in the digital space but haven't done anything yet in mobile and want to get more involved," he said.

Among retailers that have been more aggressive in setting up a mobile Web presence, Acquity selected a top 10 list that includes Amazon. com, Best Buy, 1-800-Flowers.com, Barnes and Noble, Indigo Books & Music (kobo), Sears, Overstock.com, QVC, Target and ShopNBC.com.

The criteria used to judge the companies mobile sites included the ability to detect incoming device types, whether they had mobile-specific URLs, compatibility with open-source Web content engine WebKit, and whether they used HTML5. Sites were tested on the iPhone, Android, BlackBerry, webOS and Windows Mobile platforms as well as on feature phones.

Among specific industries, companies selling flowers and gifts appeared to the most active in mobile, with 20% offering mobile sites optimized for the major smartphone operating systems, and 20% have an iPhone app.

The "mass merchant" category including major retail chains like Sears, Wal-Mart and Target was also overrepresented in having mobile-optimized sites. Nearly a third (30%) have an iPhone app and 22% have sites customized for the iPhone. Target earlier this year became the first retailer to allow shoppers to access gift card accounts nationwide from smartphones, and have barcodes scanned at checkout.

When it comes to mobile URLs, only a quarter of retailers use the "m-dot" naming convention for mobile Web addresses, with most choosing instead to use a variety of domain names. "This causes disorganization and confusion for users -- some sites even using JavaScript or long, confusing URLs to render the mobile page," according to Acquity.

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