.PWI files are files created by the notes application in windows mobile cellphones.
You can open them on a desktop PC by using MS word. I tried word 2010 only though so i'm not sure if older versions would work.
First, prepare word 2010. Open it. Go to file > options > advanced. Now scroll the right pane down to the bottom and check confirm file format conversion on open.
Now open the .pwi file with ms word 2010. In the convert file dialog box, choose Recover text from every file.
Its not perfect, there may be a few stray formatting marks like line breaks but at least the text is there.