SoftBank actually put emoji into the Private Use Area of Unicode before they were codified (just as they were in an unused area of Shift-JIS before that). The original iPhone 3GS use the PUA method.
The encoding of emoji was in order to unify Softbank/docomo/au under one set so that iPhones/Androids sold by the different carriers could send emoji among each other without relying on email translators (as had been the technical solution with feature phones until then)
The encoding of emoji was in order to unify Softbank/docomo/au under one set so that iPhones/Androids sold by the different carriers could send emoji among each other without relying on email translators (as had been the technical solution with feature phones until then)