public static void Calls()
 {
     GSM myGsm = new GSM("One X", "HTC", 800, "Georgi", new Battery("Li/Ion", 200, 7), new Display(4.7, 160000000));
     myGsm.AddCall("0878182854", 213);
     myGsm.AddCall("0898625311", 51);
     myGsm.AddCall("0898694325", 118);
     foreach (var item in myGsm.GetCallHistory)
     {
         Console.WriteLine("Call to: "+item.phoneNumber);
         Console.WriteLine("Duration: "+item.duration);
         Console.WriteLine("Date: "+item.date);
         Console.WriteLine();
     }
     Console.WriteLine("Total price: {0}", myGsm.TotalPriceOfCalls(0.37));
     //Remove the longest call
     int max=0;
     int index=0;
     foreach (var item in myGsm.GetCallHistory)
     {
         if (item.duration > max)
         {
             max = item.duration;
             index = myGsm.GetCallHistory.IndexOf(item);
         }
     }
     GSM.callHistory.RemoveAt(index);
     Console.WriteLine("Total price: {0}", myGsm.TotalPriceOfCalls(0.37));
     //Clear all history and print it
     myGsm.ClearAllCallHistory();
     foreach (var item in myGsm.GetCallHistory)
     {
         Console.WriteLine("Call to: " + item.phoneNumber);
         Console.WriteLine("Duration: " + item.duration);
         Console.WriteLine("Date: " + item.date);
         Console.WriteLine();
     }
 }