Japan already has the most advanced cell phone infrastructure in the world and it seems it will get even better and faster in the very near future. The country’s four major cell phone carriers (NTT, KDDI, SoftBank and Emobile) say they intend to invest a total of $10 billion into 3.9-generation cell phone services.

3.9G is comparable with fiber-optic networks. Japan will get the new infrastructure in the early 2010s, with the carriers planning on utilizing the existing 3G networks as much as possible to keep overall costs down. The Japanese Ministry for Communication stopped accepting applications for 3.9G licensed last Thursday and will issue them this summer.

Japan’s biggest cell phone carrier NTT aims at launching 3.9G services as early as next year, followed by the other companies in fiscal 2011 and 2012.

The picture shows KDDI ad queen Meisa Kuroki promoting a cell phone that doubles as a sports/fitness data terminal.

Via Nikkei [registration required, paid subscription]