Twelve telecom carriers kicked off today the "Myline" phone service that allows subscribers to select preferred carriers.
Intense competition in the lead up to the introduction of the system has cut three-minute local call fees to as low as 8.5 yen.
Demand for the service has been stronger than expected.
This means about 30 percent of subscribers missed its Tuesday start, according to the Myline Carriers Association, a trade body consisting of the 12 carriers.
Myline enables subscribers to connect to their preferred carrier without having to dial four-digit prefix access codes.
Subscriptions to Myline totaled about 30 million at the end of March, but roughly eight million failed to sign up in time to be able to use the service right away.
The 30 million account for half of Japan's fixed-line phone subscribers.
The larger-than-expected number of subscriptions made it impossible for the carriers to complete technical adjustments for all of the applicants' lines by Tuesday, the group said.
Many of the 12 carriers have themselves questioned the appropriateness of introducing the new service, which is certain to cut profitability.
One executive with a carrier competing against industry giant Nippon Telegraph and Telephone Corp. questioned the wisdom of plunging the carriers into an intense price-cutting war, noting that the firms face huge capital outlays to improve Internet-related services.
"What is crucial (for telecom carriers) is to expand Internet-related services," the executive said. "Is it really appropriate for telecom carriers to exhaust their financial capabilities and health as a result of rate-cutting competition?"