In May of 2000, NAR's Board of Directors adopted a policy enabling MLS participants to advertise other brokers' listings on their Web sites, with the consent of the other brokers. This policy, known as Internet Data Exchange ("IDX") or Broker Reciprocity, has been widely adopted and implemented by MLSs across the nation.

At the same time, some MLS participants have developed a business model that they've labeled a virtual office Web site (VOW) in an effort to distinguish their displays of real property listings on the Internet from the displays governed by the IDX policies.

The primary distinguishing feature of a VOW is the requirement that visitors register by entering an e-mail address and receive a password prior to accessing MLS listing data. Some MLS participants also post terms of use on their VOWs and require visitors to agree to those terms.

In large measure, VOWs have emerged in response to changing real estate business models, driven in part by the industry's embrace of the Internet as a business tool. VOW operators describe virtual office Web sites as vehicles for conducting online brokerage, allowing a company to establish and work with clients and customers in cyberspace in a way that's similar to how a brokerage interacts with its clients and customers in a bricks-and-mortar office. Viewers of MLS data on a VOW must register and, in return, typically receive more robust information on listings.

In contrast, IDX allows brokers to "advertise" each others' listings; the MLS data presented on an IDX Web site is typically less detailed, and viewers of the data remain anonymous.

Realtors who operate VOWs maintain that the registration process, coupled with the requirement that visitors agree by mouse click with the VOW operator's terms of use, take such Web sites outside the realm of an MLS's IDX rules. In fact, VOW operators maintain that by registering and agreeing to terms of use, consumers aren't simply site visitors who view real estate advertisements. Instead, they become clients or customers of the company that displays MLS listing information via the Internet.

Because clients and customers in a bricks-and-mortar office could be provided with information that includes all listings available in the MLS, including those of sellers who have prohibited Internet or other electronic display of their property as a term of their listing agreement, as well as the listings of participants who have opted out of IDX, such information is often displayed by VOW operators on their virtual office Web sites.