Select Menu > Settings > Phone > Language > Predictive text > On on your touch screen device.
With predictive text input, you can enter any letter with a single tap of a key. Predictive text input is based on a built in dictionary to which you can add new words.
You can also activate predictive text input for all text editors on the device, tap Text input indicator and select Activate prediction or quickly tap # twice.
You can also tap Input menu and select Activate predictive text.