Hi,
I was searching for app allowing to send SMSs worldwide from Japan through 3G and Wi-Fi networks, Japanese operators are controlled and prevent us from sending int`l SMSes ( we are allowed to receive it though). This one I found very good :) Easy to set up too.
Update August 25th, 2009. In spite of many updates from company they did not fix keyboard and backspace problem yet.
UPDATE September 10th, 2009 - New iPhone update 3.1 solved backspace problem :) Now JellySMS works as it supposed to, even with Japanese & other intl characters. 5 STARS !!!
Update: November 6th, 2009 - Everyone should get this app if you need to send cheap SMS not only int.
Found out recently, that one of Japanese operators allows intl SMS, but it cost ¥100 (US$1.1) per message!!! Now you know what to do :)