public static void Test()
        {
            GSM phone = new GSM("Samsung", "Galaxy S3");

            //Add calls
            GSMCallHistoryTest.Calls = new List <Calls>
            {
                new Calls(new DateTime(2015, 03, 17, 10, 32, 23), "0887591529", 35),
                new Calls(new DateTime(2015, 03, 17, 11, 32, 23), "0887595629", 56),
                new Calls(new DateTime(2015, 03, 17, 13, 32, 23), "0887576529", 39)
            };
            foreach (Calls call in GSMCallHistoryTest.Calls)
            {
                phone.AddCall(call);
            }

            GSMCallHistoryTest.PrintInfoCalls(GSM.CallHistory);

            Console.WriteLine("Total price is {0:F2}", GSM.CalculateTotalPrice(0.37));
            RemoveLongestCall(phone, GSM.CallHistory);
            Console.WriteLine("Total price without the longest call is {0:F2}", GSM.CalculateTotalPrice(0.37));
            phone.ClearCallHistory();
        }