Telecoms carrier KT has demonstrated a Mobile WiMax service that it is about to launch in South Korea.

The carrier has been using a bus to show the service, based on the Korean-developed WiBro variant of the IEEE 802.16e mobile WiMax specification.

Trials of the service began in April and a limited commercial service will kick off this month, offering up to 1 Mbit/s to users travelling as fast as 75mph. The initial service covers a single area in downtown Seoul, three areas south of the Han River in the city's IT valley, and the suburb of Bundang. A subway line and two expressways from Seoul to Bundang also have coverage.

About 150 base stations support the service now, and this is expected to expand to between 700 and 1,000 by the fourth quarter this year. At that time the full commercial service will launch in Seoul and nine other cities, according to KT's plans.

To demonstrate the service and prove it works while on the move, KT took reporters equipped with WiBro laptops and PDAs on a bus ride through Seoul. The speed challenge was difficult to test in Seoul's congested streets - we were lucky to even reach 20mph - but the data throughput was much easier to gauge.

The system managed to cope with streaming from Google Video just fine, and browsing the web was easy. KT demonstrated a three-way video conference with one participant on the bus, one in Seoul and one in Australia, and that went well and worked simultaneously with web browsing and watching a live stream of CNN.

A broadband speed-testing website estimated the connection at about 322 kbit/s, although the site was US-based, so the international connection could have impacted the speed..

There were few glitches, and the trial service seemed to fulfill its promise of being slower than existing wireless-LAN systems but with much greater coverage.

If KT and SK Telecom, which is also planning to launch a service, can deliver that for a cheap, flat monthly fee, it could provide an attractive consumer alternative to 3G data service.