The much-awaited portable-number service for cell phones has started in Japan, enabling users to change carriers without having to change phone numbers. This is a new convenience for customers, but for the cell-phone carriers -- NTT DoCoMo Inc., KDDI Corp. and Softbank Mobile Corp. -- it heralds the start of a new war. The ease with which users can change carriers is expected to cause fierce competition. It is hoped that the competition will lead to lower fees, better services and more user options.

Under the earlier system, switching carriers was cumbersome because users' phone numbers had to be changed, too. Users had to notify all their friends and acquaintances of the new numbers, often worrying that they might have forgotten somebody. With the new system, these worries are over. Phone numbers of users' friends and acquaintances, registered in the old handsets, will also be transferred to new handsets.

But users will have to change their e-mail addresses, since they are not transferable. Points earned with previous carriers as well as music, game content and other data stored in the old handsets will also be lost.