Four major Internet access providers launched Internet protocol phone services Saturday, enabling subscribers to make calls to each other free of charge.

The four companies are Nifty Corp., NTT Communications Corp., NEC Corp. and Sony Communication Network Corp. Matsushita Electric Industrial Co. will begin the service March 17.

The launch is aimed at countering Softbank Corp., which has taken the lead in the IP phone market with about 1.59 million subscribers to its broadband Internet access service.

Softbank's IP phone service enables subscribers to use IP phones with no additional charges beyond the basic fee for asymmetric digital subscriber line services.

The launch of full-scale services by the other major providers is expected to prompt more phone users to switch to IP phones from fixed-line phones. This would harm traditional telecom carriers, which rely on long-distance charges as their primary source of earnings.

Users need to have ADSL or other high-speed Internet connection services to make IP phone calls.

IP phone users pay several hundred yen in basic monthly fees, plus rental fees for hardware used for IP phones.

Calls by subscribers to any IP phone service are basically free of charge, but 8 yen is charged for three-minute calls between IP phone subscribers and fixed-line phone users, which is about a tenth of the cost of daytime long-distance calls on weekdays.