Can you text message in japanese on the iPhone in countries outside japan?

Japan's GSM network is very small, compared to the W-CDMA network that is widely used among the Japanese. The iPhone works only on the GSM network. Coverage is questionable. So, regardless of the texting, just using a GSM phone is not reliable.

You cannot text in kana on the iPhone. You can, however, enter kana in Safari if, for example, you went to a Japanese web site. There are some web sites that allow you to send SMS in Japanese, but IMHO this is not something you really want to do since it uses your data minutes instead of pure texting.

And, if you really want to get an iPhone, I'm hearing that in Japan, they're literally giving them away free when you sign up for a contract. At one source, 91-percent of people in Japan dislikes the iPhone. The Japanese are very picky when it comes to phones, so hearing that a popular phone around the world like the iPhone being disliked is quite interesting.

So in short, do not purchase an iPhone for Japan use. Purchase a Japanese phone that works on the W-CDMA network.

Largest community I'm not sure. But there are many countries in Asia that cater to the Japanese market. These countries often has signboard written in Japanese words to guide the Japanese. In addition, in the retail sector and hotel industry, many workers are trained to speak Japanese to the tourists. It is also a useful language to pick up as most companies have some form of dealings with Japanese companies, which are often multinational companies.