private static void PrintPlan(IMobilePlan plan)
        {
            Console.WriteLine("==================================");
            Console.WriteLine("You plan details is.. ");
            Console.WriteLine("==================================");
            Console.Write("Plan Name: ");

            var color = Console.ForegroundColor;

            Console.ForegroundColor = ConsoleColor.Green;
            Console.WriteLine("{0}", plan.Name);
            Console.ForegroundColor = color;

            Console.WriteLine("Plan Rate: {0}", plan.Rate);
            Console.WriteLine("Number of Free SMS: {0}", plan.SMSRate);
            Console.WriteLine("Valid for: {0} days", plan.NumberOfDays);
            Console.WriteLine("==================================");
            Console.WriteLine();
        }
        public IMobilePlan GetPlan(string planName)
        {
            IMobilePlan plan = NullObject.Instance();

            switch (planName)
            {
            case "1":
            {
                plan = new TalkTooMuch28();
                break;
            }

            case "2":
            {
                plan = new TalkTooMuch100();
                break;
            }

            case "3":
            {
                plan = new PostPaidSaver();
                break;
            }

            case "4":
            {
                plan = new PostPaidExclusive();
                break;
            }

            default:
            {
                break;
            }
            }
            return(plan);
        }