You can also pick an application to open with the HotSync® button on the USB sync cable.
To restore all the buttons and key combinations to their factory settings, select Default.
Button settings
Setting Buttons Preferences
Buttons Preferences lets you select which applications are associated with the buttons on your Treo.
1.Go to Applications 
and select Prefs 
.
2.Select Buttons.
3.Select the pick list next to the button or key combination you want to
4.Select Done.
Setting default applications
Sometimes, one application looks for another application to handle information (for example, a mail application might open a browser when you select a link in an email message).
1.Go to Applications 
and select Prefs 
.
2.Select Default Apps.
3.Select each pick list and select the application you want to associate with that function.
4.Select Done.