How to re-enable the "Clear Defaults" option for applications? I'm not able to change the default application for voice recording on my Samsung Galaxy S (running the factory installed Android 2.2).

The current settings define the one that was provide with the device (called Voice Recorder) but the "Clear Defaults" button on the Applications Management list is disabled.

Is there a way to re-enable the button? I'd try uninstalling the Voice Recorder application but the corresponding button is also disabled. Could this kind of locking be set by the operator or is this the Galaxy S default behavior?
This button is normally greyed out when there aren't any defaults set (and possibly when there are no other applications to change the defaults to).  If you install another voice recording app, you should be asked which you want to use the next time a voice recording event is triggered.  This normally doesn't get triggered when you start up the voice recorder manually, it has to be triggered.