In case you're wondering, the differences for chinese firmwares for Sony Ericsson phones is where if you have Hong Kong MAIN/FS your chinese input will be limited to strokes method and pinyin. If you have Taiwan MAIN/FS installed then your input will be strokes and "bopomofo" Taiwanese input.
So be sure to check what type of input he might use. But other than that Taiwan/HongKong all use Traditional Chinese. If you install CHINA MAIN/FS then you will have to deal with simplified Chinese.
So for me I can deal with both HongKong/Taiwan because I grew up reading Traditional Chinese. Simplified is bearable for me but I prefer the other type.