Japan's top mobile carrier said Tuesday it will invest about 5.5 billion yen in Texas Instruments Inc. of the United States to jointly develop a chip to enable cell phones to work in two different networks.

The investment from NTT DoCoMo in Tokyo will span two years through March 2006 to develop a new LSI, or large-scale integrated chip for third-generation, or 3G, phones that are compatible with both the W-CDMA network used in Japan, and the GSM standard, widely used in Europe.

Separately, NTT DoCoMo said it had developed for corporate users a 3G handset -- which also runs on wireless LAN networks -- known as an "in-house IP phone," said DoCoMo official Hitoshi Yasuda.

The handset manufactured by Japanese electronics maker NEC Corp. will cost about 400,000 yen to 500,000 yen and will go on sale this fall, he said.

Of NTT DoCoMo's 4.58 million or so 3G phone users, about 10 percent to 20 percent are corporate users.

The company is taking a risk with the dual-mode phones because users may merely take advantage of the free IP calls if wireless hot spots become more widespread that allow linking of wireless LAN networks.

Last month, Fujitsu Laboratories Ltd. and its spinoff, Net-2Com Corp., said they have jointly developed a wireless IP mobile phone handset that can automatically switch between different wireless networks.