NTT, or the Nippon Telegraph and Telephone Corporations (日本電信電話株式会社), is the largest telecommunications company in Japan for both its standard phone service and its cell phone service, NTT DoCoMo. In addition to being the largest phone company in Asia, it is the 40th most successful company and second largest phone company in the world.
The Japanese phone industry used to be solely run by the Japanese government as early as 1953, but the company itself was privatized by the same group in 1985. Despite its privatization, and despite the company being listed on the Tokyo, London and New York stock markets, the company is still partially owned by the Japanese government and majority owned by NTT.
NTT is technically the holding company. The phone industries itself are divided into NTT East, NTT West, and NTT Communications which covers the long distance and international phone calling. In addition, NTT Docomo covers the mobile phone aspect of NTT. NTT also runs NTT Data, which is a company that creates technology driven organizational systems.
NTT also invests in other companies outside of Japan, though not all of those investments have worked out in their favor. For example, NTT Docomo invested in AT&T but had to pull out at a significant financial loss. Despite that, NTT has invested in other telecommunications companies such as U-Mobile Asia (which is a mobile phone service in Malaysia).
In terms of overall revenue, NTT has the majority of its money coming in from NTT Docomo, with over 6 billion yen. NTT East is next, where it has 3.75 trillion yen in assets along with 5,860 employees. NTT West is a close third with 3.61 trillion yen in revenue followed by NTT Communications with 1.3 trillion yen, and NTT Data with 1.19 trillion yen (but over 23,000 employees). All 5 constitute the NTT group and have, combined, over 18 trillion yen (approximately 174 billion US dollars) and almost 200,000 employees. The NTT Holdings group than runs it has 7 trillion yen in assets of its own.