Only Vodafone Japan offers you the SMS service you want when you buy their 3G phones. Now it is 3yen/message, it is, however, 100yen!!!/message after the special campaign.
I guess your friends in HK or UK can use a service like e-mailing from SMS text messages to your AU e-mail account.
Unless someone in Japan has this SMS service, they can't receive a text message from a cel phone from the U.S., besides from the other countries mentioned?
just after my quick search on the net, there are some e-mail to sms hosting services available here, no matter which carriers, docomo, au, or vodafone, you use.
But the services I found were between some asian counties, north america and japan.
KDDI offers you a prepaid card service, super world card plus text. The service is not to people in Europe like I said above. But for some, it might be useful.
The frequency for japanese phones is 4 while other countries it goes up to only 3. The reason it could be happening is because your not on the same frequency as your friends are, but I could also be wrong too. I have my American phone with a frequency of 3 (tri-band) and I can use it anywhere, but japan. While my Japanese phone has a frequency of 4 and I can usually only use it over in japan. As I stated earlier I could be wrong about the reason why you can't text message people.