The Japanese mobile network operator NTT DoCoMo said it has signed up 10 million subscribers for its mobile-credit service.

DoCoMo started its DCMX service in 2006. By last March it had 5.7 million customers. They can make purchases at more than 400,000 terminals in merchant sites, up from about 250,000 in March.

Customers can spend up to the equivalent of $106 per month for DCMX "mini" without paying annual fees and up to $2,120 for the full service, DoCoMo said last week. Charges appear on subscribers' phone bills.