Dogged by a deadline to open up its instant messaging system to rivals, AOL claimed yesterday that technical hurdles have kept the company from adhering to the US government-imposed order.

On Monday AOL reached a deadline to deliver a progress report regarding the issue of instant messaging interoperability (the ability for systems to swap information).

Opening up the network was a regulatory stipulation of AOL Time-Warner's merger, which was completed at the beginning of this year. The company is not allowed to add advanced services to its instant messaging software, such as one- or two-way streaming video, until its system is open.

"I have consistently said that there are a number of difficulties with interoperability. One is security. The other is [that] no one has ever made it work," says Barry Schuler, chairman and chief executive officer of the internet arm of AOL Time-Warner. "If it's so easy to do why hasn't Microsoft done it? Why hasn't Yahoo done it?"

But the reason people are excluded from different networks could well be to force them to use one company's technology and preferably to use multiple messaging systems. Making an open network would mean people would only ever need one messaging client program on their PC. So the fact that Microsoft and Yahoo have not made an open system may have nothing at all to do with technical possibilities.

"It isn't being delayed, it's just hard to do," protests Schuler. He added that the company is "committed to launching a test of the system sometime this summer", but AOL has yet to announce any partnerships with other technology providers.

Instant messaging, he said, is one of the first and most important applications that the company can point to as a successful technology. "People are not on the telephone anymore," he says. "Instant messaging has changed the way people communicate."

But the technology has yet to surpass the telephone, as Schuler predicted it will someday. Like Microsoft's and Yahoo's instant messaging applications, AOL's ICQ and AIM, are, they claim, unable to let their approximately 30 million subscribers chat with users of competing systems.