Phone-Simple Arrays more ex.

using System;
using System.Linq;

namespace _2._4.Phonee
{
    public class Program
    {
        public static void Main()
        {
            var phoneNumbers = Console.ReadLine().Split(' ').ToArray();
           var names = Console.ReadLine().Split(' ').ToArray();

            var line = Console.ReadLine().Split(' ');

            while (line[0] != "done")
            {
                if (line[0] == "call")
                {
                    var splittedNameOrNumber = line[1].ToCharArray();
                    var isLetter = DigitOrLetter(splittedNameOrNumber);
                    if (isLetter)
                    {
                        CallingName(phoneNumbers, names, line);
                    }
                    else if (!isLetter)
                    {
                        CallingNumber(phoneNumbers, names, line);
                    }
                }
                else if (line[0] == "message")
                {
                    var splittedNameOrNumber = line[1].ToCharArray();
                    var isLetter = DigitOrLetter(splittedNameOrNumber);
                    if (isLetter)
                    {
                        MessagingName(phoneNumbers, names, line);

                    }
                    else if (!isLetter)
                    {
                        MessagingNumber(phoneNumbers, names, line);

                    }
                }
                line = Console.ReadLine().Split(' ');
            }
        }

        private static void MessagingNumber(string[] phoneNumbers, string[] names, string[] line)
        {
            for (int i = 0; i < phoneNumbers.Length; i++)
            {
                if (line[1] == phoneNumbers[i])
                {
                    var currentName = line[1];
                    phoneNumbers[i] = names[i];
                    Console.WriteLine($"sending sms to {phoneNumbers[i]}...");
                    var sumOfDigits = line[1].ToCharArray();
                    var sum = 0;
                    foreach (var x in sumOfDigits)
                    {
                        if (x > 48 && x <= 57)
                        {
                            sum += x - '0';
                        }
                    }
                    if (sum % 2 == 0)
                    {
                        Console.WriteLine($"meet me there");
                    }
                    else { Console.WriteLine("busy"); }
                    phoneNumbers[i] = currentName;
                    break;
                }
            }
        }

        private static void MessagingName(string[] phoneNumbers, string[] names, string[] line)
        {
            for (int i = 0; i < names.Length; i++)
            {
                if (line[1] == names[i])
                {
                    var currentName = line[1];
                    names[i] = phoneNumbers[i];
                    Console.WriteLine($"sending sms to {names[i]}...");
                    var sumOfDigits = phoneNumbers[i].ToCharArray();
                    var sum = 0;
                    foreach (var x in sumOfDigits)
                    {
                        if (x > 48 && x <= 57)
                        {
                            sum += x - '0';
                        }
                    }
                    if (sum % 2 == 0)
                    {
                        Console.WriteLine($"meet me there");
                    }
                    else { Console.WriteLine("busy"); }
                    names[i] = currentName;
                    break;
                }
            }
        }

        private static void CallingNumber(string[] phoneNumbers, string[] names, string[] line)
        {
            for (int i = 0; i < phoneNumbers.Length; i++)
            {

                if (line[1] == phoneNumbers[i])
                {
                    var currentName = line[1];
                    phoneNumbers[i] = names[i];
                    Console.WriteLine($"calling {phoneNumbers[i]}...");
                    var sumOfDigits = line[1].ToCharArray();
                    var sum = 0;
                    foreach (var x in sumOfDigits)
                    {
                        if (x > 48 && x <= 57)
                        {
                            sum += x - '0';
                        }
                    }
                    if (sum % 2 == 0)
                    {
                        var t = TimeSpan.FromSeconds(sum);
                        var answer = $"call ended. duration: {t.Minutes:D2}:{t.Seconds:D2}";
                        Console.WriteLine(answer);
                    }
                    else { Console.WriteLine("no answer"); }
                    phoneNumbers[i] = currentName;
                    break;
                }
            }
        }

        private static void CallingName(string[] phoneNumbers, string[] names, string[] line)
        {
            for (int i = 0; i < names.Length; i++)
            {
                var currentName = line[1];
                if (line[1] == names[i])
                {
                    names[i] = phoneNumbers[i];
                    Console.WriteLine($"calling {names[i]}...");
                    var sumOfDigits = phoneNumbers[i].ToCharArray();
                    var sum = 0;
                    foreach (var x in sumOfDigits)
                    {
                        if (x > 48 && x <= 57)
                        {
                            sum += x - '0';
                        }
                    }
                    if (sum % 2 == 0)
                    {
                        var t = TimeSpan.FromSeconds(sum);
                        var answer = $"call ended. duration: {t.Minutes:D2}:{t.Seconds:D2}";
                        Console.WriteLine(answer);
                    }
                    else { Console.WriteLine("no answer"); }
                    names[i] = currentName;
                    break;
                }
            }
        }

        private static bool DigitOrLetter(char[] splittedNameOrNumber)
        {
            return (splittedNameOrNumber[0] >= 'A' && splittedNameOrNumber[0] <= 'Z') || (splittedNameOrNumber[0] >= 'a' && splittedNameOrNumber[0] <= 'z');
        }
    }
}