Those are done in their individual app:
Originally Posted by Tomween1
Email notifications, open the email app, tap on menu and go to preferences and accounts. Tap on your email account and change the alert to system sound or ringtone of your choice. You can also have seperate sounds for each email account on the device if you want.
For messaging, open the messaging app and go into preferences and accounts. Change the alert to system sound or ringtone of your choice.
For skype calls, go into the Sound and Ringtons app and set the ringtone there.