Known as DCMX, the service was launched in April 2006 and enables users to make purchases by using their mobile phones as credit cards through its iD platform.
There are around 420,000 readers across Japan, meaning owners of compatible phones can pay for taxis, restaurants and shopping without needing cards or cash.
The operator, which has over 54 million phone customers in Japan, said that it reached one million subscribers seven months after the service was launched, before acquiring five million users in February 2008.
It noted that the "rapid penetration" of the service has been aided by its customer loyalty program, which offers users reward points each time they make a transaction using DCMX.
Earlier this month, City University London received a $222,000 grant that will be used to develop new ways of increasing the security of online banking.
Written by Claire Archer