Palm G18 Delete forever:

Using the SMS Short Message
G18 User Manual 82
In the dialog box, tap the OK button, then delete the message; tap the
Delete All button, then the all message in the directory will be deleted, tap
the Cancel button , then canel the operation.
Delete forever:
Tap the MENU icon, then a pick list will appear.
In the list , select the Empty Trash , then delete all the message saved in
the dustbin.
tap "Empty Trash"