Sub fixfax()
Dim i As ContactItem
  For Each i In ActiveExplorer.Selection
    If Len(i.BusinessFaxNumber) > 0 Then i.BusinessFaxNumber = "fax:" & i.BusinessFaxNumber
    If Len(i.HomeFaxNumber) > 0 Then i.HomeFaxNumber = "fax:" & i.HomeFaxNumber
    If Len(i.OtherFaxNumber) > 0 Then i.OtherFaxNumber = "fax:" & i.OtherFaxNumber
    i.Save
  Next
End If
End Sub