eBay ( EBAY) chief Meg Whitman, whose Web site lets people buy everything from DVDs to boats, has plenty of selling to do.

Whitman is due to address investors Thursday morning at a Credit Suisse First Boston conference in Phoenix. With Wall Street already concerned about eBay's growth, the CEO now faces criticism from a group of big eBay users who are miffed over Whitman's latest strategic stroke.

In October, eBay acquired closely held Internet phone company Skype in a move Whitman said would "create an extraordinarily powerful environment for business on the Net." But that message hasn't resonated with some of eBay's biggest sellers.

"Skype doesn't give me a capability that I already don't have," says Jonathan Garriss, executive director of the Professional eBay Sellers Alliance, a group of about 900 high-volume eBay sellers. "It's not something that is going to change the way that the eBay sellers in our group are going to run the business."

Garriss, who says his information comes from informal conversations with members, says many high-volume eBay users won't sign up for Skype because they prefer to communicate with customers via email. eBay stresses that the acquisition serves purposes beyond matching users of its Web sites, but the sellers' comments underscore the challenges eBay faces in integrating the phone service with the rest of its operations.

Lingering concerns about eBay's growth prospects and the hefty price tag for Skype -- $2.5 billion plus earnouts that could push the tab as high as $4 billion -- have hammered eBay this year. Its shares have dropped 20% even as rivals Google ( GOOG) and Yahoo! ( YHOO) have soared.

eBay's third-quarter sales jumped 37% from a year ago to $1.1 billion, but the 30% rise in the value of goods sold on eBay's sites marked the smallest year-over-year increase in at least two years. Yet shares of eBay fetch a multiple of about two times its price-to-growth rate for 2006, which is higher than both Google and Yahoo!.

"People believe that the U.S. market will show some signs of deceleration next year and that international markets such as China won't accelerate fast enough to make up for it," says Martin Pyykkonen, an analyst with Hoefer & Arnett who rates eBay shares reduce and doesn't own them.

Skype, which was founded in 2002, wasn't profitable when eBay purchased it and will dilute the company's earnings for the next two years.

"There really is no obvious connection between the two businesses," said Darren Chervitz, director of research for New York-based Jacob Asset Management, which owns shares of eBay and TheStreet.com ( TSCM), publisher of this Web site. "Skype may end of up being a valuable business, but I am not 100% sure it will be because eBay owns them."

With users in 225 countries and territories, Skype has developed a loyal following with very little advertising. Skype claims that its service is the fastest-growing communications application, adding more than 150,000 users per day. It has been downloaded more than 212 million times, according to Skype's Web site.

Skype may help eBay compete against rivals such as Google, which is testing an Internet phone calling system called Google Talk. Cable companies including Comcast ( CMCSA) and Time Warner ( TWX) also have entered the so-called voice over Internet protocol phone market.

TeleGeography estimates that the number of U.S. VoIP subscribers rose 400% from a year ago in the third quarter to 3.6 million. Revenue rose 473% to $304 million.

Though the gains are impressive, they still represent a small fraction of the overall telecommunications market and many users show no interest in changing from conventional phone service, says Maribel Lopez, an analyst with Forrester Research, who follows the Internet phone market.

"At this point, nobody in the VoIP industry has made a good solid case for the value, and the acquisition of Skype by eBay complicates matters," she says.