Mobile phone service operators will be required to remove carrier-specific restrictions, or SIM locks, on handsets starting Friday.

The move is expected to spark price and service competition in the domestic mobile phone market as users will be able to switch carriers more easily without having to replace their handsets.

Until now, most mobile phone subscribers in the country had to buy expensive handsets when they changed carriers, while many countries in Europe and the United States have already abolished SIM locks.

The removal of restrictions could lessen the market dominance of major carriers and make it easier for customers to use inexpensive services offered by mobile virtual network operators that lease and resell network capacity from major carriers.

NTT Docomo Inc., the biggest mobile phone carrier here, has announced it will remove SIM locks on handsets that customers keep for more than six months after they buy them.

KDDI Corp. has followed suit, while SoftBank Corp. is also preparing to announce a policy on phasing out the locks.