A NEW communications technology that uses spare capacity in television transmissions to deliver point-to-multi-point broadcast fax services is to be launched in Hongkong later this year. An international consortium, known as Faxcast Holdings, is looking for a Hongkong-based firm to provide the local link of an ambitious global fax service, which will eventually allow subscriber-based fax services to be sent simultaneously all over the world. The service uses a ''black box'' decoder technology developed in Canada by Faxcast Broadcast Corp to receive fax services delivered within the ''vertical blanking interval'' (VBI) of a television broadcast interval. Television signals are broadcast at 25 frames per second, with each frame divided by a ''blank'' broadcast space. ''That space is blank of video and blank of sound,'' said Faxcast Broadcast chairman Mr Robert Towning. ''The data that we send is sent in that space.'' The ''black box'' sits between the television receiving antenna and the fax machine (or personal computer with faxcard), decoding data sent within the VBI. The fax machine can also be hooked up to the standard telephone line. If the fax machine is engaged at the time of the message broadcast, or for any reason is temporarily out of commission, the Faxcast box, with four megabytes of random access memory, automatically stores the message, to be downloaded later. Faxcast Broadcast is looking to develop a global network using the technology, setting up individual partnerships in each country market. Ultimately, the company expects to offer a service that allows broadcast fax to be delivered virtually anywhere in the world. The company is at various stages of system trial in the United States, Britain, Australia, New Zealand, Switzerland, Sweden, and South Africa with franchises imminent in Hongkong and Thailand. Initially, the company expects to sell the service to close user group applications, such as travel agents, constantly receiving pricing and scheduling updates from airlines, or banks that may need to fax directives to branches across a whole region simultaneously. The company also hopes to promote subscriber-based information services that can be delivered through the system - such as fax versions of daily newspapers, or subscription-based financial newsletters; all of which are delivered to customers simultaneously. Mr Towning said the ''black box'' decoders would be rented to customers at about US$20 per month, with subscriber services paid for on top of that. He said that Asia was following the trend in North America, where expenditure on fax-based information services was forecast to grow from $250 million in 1991 to $1.2 billion in 1995. ''The fax market worldwide is growing at 100 per cent per year and Asia has one of the highest penetrations of fax machines,'' Mr Towning said. ''We consider this region a very important part of our plans for a global network. The increasing use of the fax as a publishing tool, as well as a means of instant mail, is revolutionising the communications environment,'' he said. The company claimed it could deliver fax messages far more cheaply than the more traditional store-and-forward service providers, particularly over long distances. The per-page charge for using the service would be decided on a country-by-country basis, Mr Towning said. ''As a corporate philosophy, we expect to act very aggressively in price to achieve maximum market penetration as quickly as possible,'' he said. ''We really need to reach a critical mass of customers as quickly as possible.'' The company hopes to name a Hongkong Faxcast ''distributor'' this summer.