Microsoft last week introduced its MSN Messenger tool with the ability to exchange instant messages with of AOL Instant Messenger users, but AOL last Friday changed its system to lock out Messenger and other competing applications from Yahoo! Inc. and Prodigy. MSN has released updates of Messenger that get around AOL's blocks -- AOL has been countered all of them; a Microsoft representative said that the version of Messenger released Wednesday was the fifth in as many days. As of Thursday morning there was no new workaround available from Microsoft. Also on Thursday, some users began protesting America Online Inc.'s instant-messaging tactics. "Boycott AIM" urges users to strike a blow for interoperability by circulating a chain e-mail and signing a petition. So far, though, the boycott campaign has yet to get off the ground, with only a few dozen visitors to the Web site. At first glance, it might appear that the battle that continues to simmer between the two companies is about good open standards versus evil proprietary standards. Microsoft has taken the position that it is supporting open, freely available protocols, while AOL is left to defend its proprietary messaging system. But in a larger sense, industry observers say, what's at stake is the continued development of a new kind of technology, pioneered by AOL and its subsidiary Mirabilis, that recently became more popular than the U.S. Postal Service. A widely-used standard can be crucial to helping a new technology develop, because it lessens the distractions of competing platforms. Right now, instant messaging is dominated by AOL's proprietary standard, analogous to Microsoft's Windows platform in the operating-system universe; but industry watchers predict that IM will ultimately evolve into an open system, like the protocols of the Internet. "The standard is already there, it's just not one that's open," said analyst David Card of Jupiter Communications. "Microsoft is trying to crack open that network, but it's waving the open systems flag before there really is such a thing." Instant messaging is a fundamentally new communications technology, allowing users to make notes pop up in real time on other users' screens. It's become a huge success, with the number of IMs sent per day recently surpassing the volume of letters handled by the Post Office, and that has led several companies to attempt to cash in on the business. Microsoft set things off with the release of its MSN Messenger software last week, which lets users connect to AOL IM users as well as those on MSN. (The company reported Wednesday over 700,000 downloads of the product.) Every instant messaging system is separate at present, allowing users of one product to connect only to other users of the same product. Also late last week an AOL executive, network security chief Tatiana Gau, sent a letter to Microsoft suggesting the two companies negotiate a deal. Microsoft vice president Brad Chase responded in a letter Tuesday inviting America Online to take part in the process of building an open standard for instant messaging. The Internet Engineering Task Force (IETF) is currently devising such a standard, with Microsoft's active participation, but nothing is expected to be finalised for months. Microsoft has not itself built open standards into Messenger, meaning, for example, that AOL users cannot send instant messages to MSN users. In fact, to access AOL's messaging system, MSN users must first register separately with AOL. The IETF sees open standards as a way to make all instant messaging systems compatible, making the technology potentially as ubiquitous as the telephone. "This is a big deal, and just as HTTP and HTML were the foundations of the Web, this is the next step beyond the Web," said said Vijay Saraswat, a researcher for AT&T Labs and the co-chairman of the IETF task force, in an interview with ZDNN Executive Producer Patrick Houston. "It brings interaction into the very heart of people's experience of the Internet." In the meantime, Microsoft would like AOL to open up its own de facto standard. But AOL responds that it is open to licensing its system to other companies, as long as it is kept in the loop. "Two years ago, voluntarily, as the Internet started to emerge, we opened our system," said Barry Schuler, president of America Online's Interactive Services Group, in an interview with ZDNN senior executive news editor Charlie Cooper. "We've been very cooperative with people who wanted to do deals with us. For fair and not onerous deals, we're happy to talk to anybody."