you make the point very well! You can still remember, what, 20 years later ?
On the nokia you'd press the button and it would cycle through the options. Once you knew all the words you could type really very fast indeed, and blind.
Someone asked about custom words below. You could definitely add custom words. I think you had to switch out of T9, key the word the old way and then switch back then 'add' to dictionary, but once in it would stay in the dictionary. I'm sure the amount of memory for custom words was quoted in marketing material at somepoint.