There is no Sort property or method for ListBox on the device.
There is one for the desktop, but it needs the Door library.
You can first put your data in an ArrayList, sort it and then transfer the sorted data to the ListBox.
And here is a code that implements klaus suggestion:
B4X:
Sub Globals
'Declare the global variables here.
End Sub
Sub App_Start
Form1.Show
SortListBox("ListBox1")
End Sub
Sub SortListBox(List)
ArrayList1.Clear
For i = 0 To Control(List,ListBox).Count-1
ArrayList1.Add(Control(List,ListBox).Item(i))
Next
ArrayList1.Sort(cNumbers)
Control(List,ListBox).Clear
For i = 0 To ArrayList1.Count-1
Control(List,ListBox).Add(ArrayList1.Item(i))
Next
End Sub
It uses an ArrayList named ArrayList1 to sort listboxes. Depending on your type of data you may need to change the line: