In the thumb board, I start to type words and the N800 guesses the correct ending. However, I can't figure how to accept its suggestions. There's no completion button to hit as in the small keyboard. No matter what I type or where I type the screen, it just erases its proposal.

I use the dpad on the right..... IF you press the right direction of the d pad the word it predicts comes up. Another way with less precsion is swiping the word with your finger along the predicted word... it does not work all the time

just CLICK on the word

Word: Environment

you type "Envir"

you will see: Environment

click on the onment part. Voila

How do you click on the completion? If I touch the completion, it disappears. It works fine in the small keyboard, where the completions are clickable buttons at the bottom. But not in the thumb board, where it just suggests one completion.

The previous poster suggested to use the right side of the d button. That does work. Only downside is having to move finger far off keyboard.

Come to think of it, I'd like to cycle through possible completions as well in the thumb board.

if you click CLOSE to the completion then it will go away, if you click directly on the suggestion it will be selected. I do it all the time.

I will admit it is harder to click on in thumb board, as it's easy to misclick or the keyboard doesn't recognize you clicking directly on the word and not whitespace.... but it works