Service was lost in Tokyo and surrounding areas from 10:40 p.m. local time Tuesday and did not return until 2 a.m. Wednesday morning, NTT DoCoMo said in a statement. The company suspects problems at its data center in Tokyo were at the root of the problem and 514,000 customers were inconvenienced by the inability to send and receive e-mail or view Web sites using their cellular telephones.
The breakdown comes less than a week since a five-hour long nationwide failure of the service, and in the same month that the operator proudly declared it had attracted more than 10 million users to the service.
Problems have been plaguing the system since April this year when the growing number of users -- at that time I-mode had just over 6 million subscribers -- began proving too much for the system. The company said engineers had designed the system to accommodate 14 million subscribers although strains had begun to show late each night as many users began using the service from home.
The company went as far as stopping promotions for I-mode during May in an attempt to slow subscriptions and only began full-scale marketing in late May when it assured users the problems were solved.
Still, problems continued especially late at night as users crowded the system. In response, NTT DoCoMo is busy trying to add capacity and build new data centers to accommodate users. I-mode had 10.3 million users as of August 13th.