today's FAQ is about getting the full postcode search to work on your device. Please follow the steps below and you'll have the postcodes available on your device afterwards.
Please if you don't know check the installed map version first.
How to check the map version (hyperlink)
Now please download the appropriate postcode file and save it to your computer without changing the file's name.
Now, please open that file using i.e. WinRAR.
After having done that please extract the file to a folder called zip (all letters lower case).
Having extracted the file please copy that folder called zip and containing the postcode files to the root folder of your device.
Now that the files are on your device please open TT Home and disconnect your device safely from the computer using the blue button in the bottom right corner of TT Home. After having disconnected safely you'll be able to use the full postcode search on your device.
Edit (Mikko): There's also a support FAQ including instructions for different OS versions here.