Works very well for me. I'm using OS 5.0.0.238 and it works there. What OS are you using? Try checking in your Options | Applications listing, if you see it in there, delete it, then pull the battery. When the phone comes back up, then go to
Download | Viigo from your mobile browser.
Note that you have to select the correct version of Viigo to download, either for BIS or BES.