The DDI Pocket Telephone Group, comprising nine companies, rolled out commercial PHS service in July 1995. At the end of January 1997, the Group as a whole had signed up some 2.4 million subscribers. It was providing service in 688 cities throughout Japan at the end of February 1997, of which 293 municipalities were located in the greater Tokyo area. DDI Pocket's service areas now covers approximately 75% of Japan's population.

From the outset, DDI Pocket adopted a large-zone system with cell station output of 500mW, based on its own technology. Cell station antennas have mainly been installed on building rooftops with the aim of expanding the coverage area and also enabling radio signals to penetrate inside buildings. Recently, DDI Pocket has also been installing small-zone cell stations with 20mW output in heavy traffic areas, in a move to expand its service areas efficiently. DDI Pocket now has some 40,000 cell stations in place nationwide, with approximately 16,000 installations located in the Tokyo area .




April 1997, DDI Pocket launched data transmission service using the PIAFS protocol explained elsewhere in this issue. DDI Pocket also provides data transmission services using its own protocol, in addition to PIAFS. From the time it began operating, DDI Pocket incorporated a media conversion capability (14.4 kbps analog modem) in its cell stations in anticipation of demand for data communications services. Data service at a speed of 14.4 kbps was initiated in December 1996, and a 32-kbps service was added in April 1997.
All that is required for these services is the use of a dedicated Data PC card to connect a notebook PC or other device to a PHS terminal. PC communications service companies and Internet access providers do not have to install any special equipment. This means that existing equipment can be connected to access points without an intervening adapter. These data services are offered at the same rates as voice services. PHS terminals compatible with either the PIAFS or DDI's data protocol can now be used to obtain DDI Pocket's data services.

December 1996, DDI Pocket began providing a low-cost data communications service at a uniform rate nationwide regardless of the distance to the access point. This service is available through an interconnection with the Multimedia Access Line (MAL) data communications service provided by DDI Corp., the long-distance telephone company that owns DDI Pocket. For users of Internet access providers connected to DDI's MAL, the charge to the access point is a uniform 13yen (11cents US) per minute all day long anywhere in Japan. While charges generally rise as the distance to the access point increases, users of DDI-MAL can access the network from anywhere in the country at the same cost using the same number.
Text messaging function of PHS terminals has so far depended on each manufacturer's own technology. Consequently, PHS terminals made by different manufacturers have been unable to exchange text messages. To eliminate this inconvenience, DDI Pocket adopted a PHS specification as its unified messaging protocol. As a result, DDI Pocket subscribers with PHS specification terminals can now exchange text messages of up to 20 characters in length. A function is also provided that enables the sender to confirm that a message was received. The rate for sending a message is 20yen (17cents US). All the terminals sold by DDI Pocket in the future will be equipped with P-Mail capability.