By Nam In-soo

SEOUL (Reuters) - South Korean mobile operator KT ICOM Co showed on Wednesday that users of its third-generation service would be able to make video calls from abroad, in what it said was the world's first demonstration of video roaming.

Roaming, which enables customers of different carriers to use each other's networks when they travel, will be crucial if 3G is to become widely accepted. Roaming has so far been limited to voice traffic and simple photo swapping.

KT ICOM officials in Japan used their phones to make a video call to colleagues at a press briefing in Seoul. The phones in Japan, which contained SIM cards from the South Korean company, roamed onto the local network of J-Phone Co.

"Hello there, it's nice to meet you over the mobile phone,"

KT ICOM President Cho Young-chu said to a J-Phone official in Japan, speaking into a clam-shell phone with an embedded camera and a business card-sized screen showing both callers.

"Nice to see you," said John Thompson, executive corporate officer of J-Phone, whose voice became clear after a buzz in the first minute.

KT ICOM, the 3G unit of KT Corp 30200.KS , said it planned to offer a full-scale commercial 3G service based on W-CDMA (Wideband Code Division Multiple Access) technology in the first half of 2003.

The technology is expected to provide access to the Internet, music downloads and streaming video at five to 25 times faster than current 2G mobile networks.

"In 2G technology, we were behind our competitors in Europe and other countries," said Hahn Choon-Koo, director of Korea's Information Ministry. "But we will lead the pack in 3G services and the government will spare no efforts to help local carriers and equipment manufacturers."

KT ICOM's network equipment was provided by South Korean firm LG Electronics Inc 66570.KS , while J-Phone used kit from Sweden's Ericsson LMEb.ST . LG provided the 3G phones to both companies for the trial calls.

J-Phone, Japan's number three wireless operator, is a joint venture between Japan Telecom Co 9434.T and Britain's Vodafone Group Plc VOD.L , the world's largest mobile carrier. It plans to launch 3G in December.

South Korea, which has helped pioneer CDMA mobile technology, has one of the world's fastest growing mobile service markets. Operators say around 13 million of their more than 30 million customers regularly use mobile data services.

Korea's top mobile carrier SK Telecom 17670.KS and two other carriers began CDMA EV-DO services early this year, which can transmit and receive data at hitherto unheard-of speeds of up to 2.4 megabits per second.

That's around seven times faster than the world's first 3G service launched last October by Japan's NTT DoCoMo Inc 9437.T .

World Cup co-hosts Korea and Japan used the soccer tournaments to showcase their advanced wireless services.

At the ceremony before the opening games in Seoul on May 31, the stadium's giant screen flashed images of spectators that were wirelessly relayed by the same LG phones used for the roaming demonstration.