NTT or Nippon Telegraph and Telephone is the parent company of Japan's largest carrier, NTT DoCoMo. This company is actually world's largest telephone company if we look at revenue. Unfortunately for them, their international investments didn't exactly go as planned, the company has lost a significant amount of money over the years. The company recently divested its stake in Tata DoCoMo, an Indian Carrier, of which they owned about 26%. NTT has invested over $2.5 billion dollars in Tata DoCoMo and had to face loses considering the poor financial results of that company. Nippon Telegraph and Telephone has invested in AT&T a long time ago, they ended up selling their multi-billion dollar investment in 2002 and had to face a significant loss in the process. They shouldn't have done that at the time considering AT&T financial performance after they did that, of course they couldn't have known what will happen afterwards and have tried to save at least a part of their initial investment.
NTT is opening a new research center and a showroom in Silicon Valley along with bringing local talent in to bring the business on its feet. 90% of NTT's revenue is coming from Japan at the moment, so they've been trying to diversify a bit and increase their overseas revenue in order to achieve some sort of balance and increase company's growth of course. NTT has some other investments all over the US, mostly hard infrastructure (they have other IT-based investments as well), though their main focus is Silicon Valley at the moment. NTT will probably switch to the wireless sector sooner or later, as a main goal. Mobile business is the thing to invest in these days and it is definitely the future, basically everyone can see that. I wouldn't be surprised if NTT decides to increase its stake in one of current US carriers or even acquire one of them. Who knows, maybe NTT joins the race for T-Mobile in the near future. That is just a guess of course, but it seems somewhat logical, especially if they want to expand their mobile business abroad.