Japan is moving towards ending restrictions on mobile telephone users switching operators or using an overseas network by changing the SIM memory card, a government official said Monday.

The government has launched a review of the "SIM lock" system used by Japanese cellphone carriers to prevent people from using a handset from one operator on a rival network by replacing the SIM card.

A SIM, or subscriber identity module, card is a portable memory chip that fits into a mobile telephone and allows the user to access the service provider's network, as well as storing personal data.

Japan's three major mobile service carriers currently sell handsets that accept only their respective SIM cards.

This means Japanese people travelling overseas cannot fit SIM cards of local carriers inside their Japanese handsets and must instead use the international services of their Japanese carriers, or buy a new phone.

Kazuhiro Haraguchi, the communications minister, has questioned the need for the restriction and the government will hold a meeting Friday to hear from businesses and consumers on the issue.

"The minister has issued an order to review the role of SIM lock," a communications ministry official said.

Japan's top mobile carrier NTT DoCoMo, however, reacted cautiously to the review, saying "careful discussions" were needed.

"We provide unique service features other than voice calls. They are possible because of unique handsets," a DoCoMo spokesman said, referring mainly to special Internet and networking services.

"Abolishing SIM lock could limit the types of services we provide," he said.