Sub ConverToText()

    Dim c As Range
    Dim AppCalcMode As XlCalculation

    Application.ScreenUpdating = False
    AppCalcMode = Application.Calculation
    Application.Calculation = xlCalculationManual

    For Each c In Selection.Cells
        c.Value2 = Chr(39) & c.Value2
    Next c

    Application.Calculation = AppCalcMode
    Application.ScreenUpdating = True

End Sub