Welcome to Pocket PC Thoughts.
I recommend checking out the "interface workflow" section in
this Wiki entry.
In a nutshell, each key corresponds to a group of letters, though you only need to press a key once to get a particular letter. For example, if I wanted to type "hello", I'd ensure that the phone is in T9 mode and then type "43556". The phone would predict any possible word combos, and "hello" would be one of them. It's different to the "abc" text input scheme which requires you to press the key a number of times to get a certain letter. Under an "abc" scheme, "hello" would be "4433555555666". So T9 can be a real timesaver.
