public static void TestCallHistory()
{
Call call0 = new Call("31.3.2015 9:08:33", "00359 888888", 60);
Call call1 = new Call("01.4.2015 22:19:04", "+44 123123", 578);
Call call2 = new Call("02.05.2016 02:16:00", "02 967 2323", 134);
gsm.AddCall(call0);
gsm.AddCall(call1);
gsm.AddCall(call2);
gsm.ShowCallHistory();
decimal pricePerMinute = 0.37m;
Console.WriteLine("Total price: {0:C}", gsm.CalculateTotalPriceOfCalls(pricePerMinute));
gsm.DeleteCall(1);
Console.WriteLine("Total price: {0:C}", gsm.CalculateTotalPriceOfCalls(pricePerMinute));
gsm.ClearCallHistory();
gsm.ShowCallHistory();
}