Chinese on a mobile
Just because I accidently know:
There are 2 ways to enter chinese characters on a phone (with Chinese character support).
All Chinese characters are made up of a set number of 'strokes' or lines. The strokes are all uniform (straight horizontal line, straight vertical line, curved line from top to down right etc) and there are maybe 8 possibilites. When you're writing a character you must write the strokes in the correct order, and so by pressing the key strokes in the correct order there are a finite number of possible character matches. For example the keystroke combo 1,3,4 (horizontal line, curved line to the left, curved line to the right) gives 2 possibilites, the most common of which is 大 (da, meaning big).
The other method (more popular with me) is one involving Pinyin, or the phonetic version of Chinese characters.
Each character can be represented by a single syllable sound, link 'dong', 'xi', 'nan', 'bei'. There are not many of these sounds (maybe 50 possibilities? I forget) but anyway so each of these sounds represents a different number of characters (sometimes maybe 20 different meanings). Sounds difficult, but actually the most common ones are very common, and the phone dictionary knows this, so if I type in 'yang' it knows I mean 羊 (sheep) and not 痒 (itchy) since one is common and one is not. It's just like T9. It still offers you the full list of words (if you do want to say that your inner-leg needs a scratch).
Hope this sheds some light on the questions. Other quick info - texts are limited to 70char (although using characters means a huge amount of extra info can be sent) and a text costs 1mao = 1/10rmb = 1p to send.