C# .NET - How to validate phone no( ex; (123) 456-7890) in .Net?

using System;
using System.Text.RegularExpressions;

namespace _11_RegularExpressions
{
  class Class1
  {
    [STAThread]
    static void Main(string[] args)
    {
      Regex phoneExp = new Regex( @"^\(\d{3}\)\s\d{3}-\d{4}$" );
      string input;

      Console.Write( "Enter a phone number: " );
      input = Console.ReadLine();
      
      while( phoneExp.Match( input ).Success == false )
      {
        Console.WriteLine( "Invalid input. Try again." );
        Console.Write( "Enter a phone number: " );
        input = Console.ReadLine();
      }

      Console.WriteLine( "Validated!" );
    }
  }
}

function isPhoneNumber(s)
{

     // Check for correct phone number
     rePhoneNumber = new RegExp(/^\([1-9]\d{2}\)\s?\d{3}\-\d{4}$/);

     if (!rePhoneNumber.test(s)) {
          alert("Phone Number Must Be Entered As: (555) 555-1234");
          return false;
     }

return true;

This is what your ValidationExpression property should look like:  

((\(\d{3}\) ?)|(\d{3}-))?\d{3}-\d{4}( x\d{0,})?

 Copy and paste this string into the ValidationExpression property of your Regular Expression Validator control. What I did was add “( x\d{0,})?” to the end of the string (without the quotes) that Microsoft provided for us. My example allows a user to enter a phone number with an extension formatted as: (770)123-4567 x1234. If you prefer to use “ext” for extension, simply edit the above string and replace “x” with “ext”. Make sure that your database field is big enough to accommodate the entire phone number and extension – at least varchar(25) in our case.