BlackBerry fast typing using the Autotext feature.
To help you with this problem the BlackBerry's Autotext feature makes the corrections on the fly. It keeps a list of the most common typos and associates them with their correct spelling. So, while you are typing, Autotext checks each word and if it finds a typo (that it has in its list) it makes the replacement with the correct spelling.
For example: if you typed the word acn you'll see that as soon as you pressed the SPACE key or ENTER, the text will change to can. Note that this works only for separate words i.e. if you type acn as part of a bigger word the correction will not take place.
Starting from this simple and efficient idea, Autotext has added in its list of typos other common situations that could help you in your typing. For example: if it finds the word cant it assumes that you wanted to type can't. The same is true with: arent, couldnt, isnt, etc.
Anybody can see the Autotext list of associations, by navigating: Settings then Options then selecting Autotext and opening it.
Autotext doesn't stop here, though. It allows you to easy change the existing associations or to add new ones. Usually you add new entries to easy the typing by using abbreviations. For example, I've added a new entry named aa and associated it with http://www.ghcb.blogspot.com. From now on if I want to type the address of my blog I just type aa.
Autotext is cool, since it allows you to use your imagination in choosing abbreviations and then use your memory to remember them :)
If you want to read more, see Typing section in the BlackBerry 7100 Series User Guide that you can download from here.