For example.. One of my Japanese friend gived her cell phone e-mail.
I was trying to send to her e-mails from my yahoo.com and its didn't worked.
My friend was also trying to send from his e-mail to mine yahoo.com.
But guess what... When I created japanese e-mail. And sended e-mail to my friend. My friend got it and was able to send stuff back.
That not because of "cool factor"... lol
I've seen this before. Japanese cell phones are picky about what type of mail they can receive, because they don't have support for all languages built in. When a Japanese e-mail server sends mail, it explains that it is Japanese. Some English e-mail servers will claim their mail is English (even if there's only Japanese in it), and since the Japanese cell phones don't recognize the English type (some only do utf-8 and Japanese), they simply won't display the mail and won't even give an error message.
I had to change my hotmail interface to Japanese before my old J-Phone would accept e-mails from it.