A telecommunications ministry study panel adopted a draft proposal Thursday that the ministry introduce a system to enable mobile phone users to retain their numbers when switching from one service provider to another.

The proposed "number portability system" could be put into practice in fiscal 2005 at the earliest, ministry officials said.

The draft was drawn up by a research panel led by Tadao Saito, a professor emeritus at the University of Tokyo.

The panel, which comes under the Public Management, Home Affairs, Posts and Telecommunications Ministry, will compile a final proposal in late April after soliciting opinions from the public, the officials said.

After receiving the final report, the ministry will start working with mobile phone companies to make preparations for introducing number portability, which is already in use in some countries in Europe and Asia, as well as in the United States.

Industry analysts said the new system will benefit users but may intensify competition between mobile phone companies to prevent their subscribers switching over to rivals.

NTT DoCoMo Inc., Japan's largest wireless carrier, has remained reluctant to agree to the new system, saying it would require an estimated 100 billion yen in costs to alter software programs.

In an industry survey last year of mobile phone users, 37 percent of the 2,683 respondents said they would consider changing carriers if they had the ability to take their number with them.