Input Phone Number Formatting

using System;

class Tel
{
    public static void Main()
    {
        string tel = "";
        Console.Write("Tel. +359 ");
        ConsoleKeyInfo key;

        do
        {
            key = Console.ReadKey(true);

            if (key.Key != ConsoleKey.Backspace && key.Key != ConsoleKey.Enter)
            {
                tel += key.KeyChar;
                double telForm = double.Parse(tel);
                Console.Clear();
                Console.Write("Tel. +359 {0:### ## ## ##}", telForm);
            }
            else
            {
                if (key.Key == ConsoleKey.Backspace && tel.Length > 0)
                {
                    tel = tel.Substring(0, (tel.Length - 1));
                    Console.Write("\b \b");
                }
            }
        } while (key.Key != ConsoleKey.Enter);
    }
}