To make stop an app being a “default application” for a certain type of action, do this:
1. Menu –>Settings –> Applications –> Manage applications.
2. Find your application in the list and click on it
3. Scroll down in the page and click Clear defaults button
4. Next time you open similar app associated with this app (the one that you clear defaults), you will be presented with a pop-up letting you choose what app you want to use.
WaveBoy2u 