Sub cmdPreview_Click()
    On Error GoTo HandleErrors

    ' There are three possible scenarios:
    '  1 . No filter
    ' 2. Filter, but not applied
    '  3 . Filter, applied
    
    Dim strFilter As String
    
    ' The following statement
    ' works for all three cases.
    ' If there's no filter, or
    ' it's not on, strFilter will
    ' be an empty string.
    If Me.FilterOn Then
        strFilter = Me.Filter
    End If
    
    DoCmd.OpenReport ReportName:= "rptPhoneBook" , _
     View:=acPreview, _
     WhereCondition:=strFilter

ExitHere:
    Exit Sub

HandleErrors:
    Select Case Err.Number
        Case  2501 
            MsgBox  "There are no rows to display!" 
        Case Else
            MsgBox Err.Description
    End Select
    Resume ExitHere
End Sub