>Cetin,
>
>You are a prince!
>Thank's a lot and a prosperous and happy new year to you and yours.
>
>BR

LOL. Thanks for your kindness Peter. Here is the sample I promised (I had a SSN like validation code ready):

using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
using System.Text;

namespace CBSQLUserDefinedFunctions
{
    public partial class Transformer
    {
        /// <summary>
        /// 9: Allow digit only
        /// A: Allow letter only
        /// !: Convert to uppercase
        /// N: Allow Digit or Letter
        /// U: Allow letter only and convert to uppercase
        /// W: Allow letter only and convert to lowercase
        /// X: Allow any character
        /// Any other character is copied as is for display
        /// </summary>
        [Microsoft.SqlServer.Server.SqlFunction
            (DataAccess = DataAccessKind.None, IsDeterministic = true)]
        public static SqlString Transform(string value, string mask)
        {
            byte[] result = new byte[mask.Length];
            for (int i = 0, j = 0, k = 0; j < mask.Length; j++, k++)
            {
                switch (mask[j])
                {
                    case '9':
                        while (i < value.Length && !Char.IsDigit(value[i])) { i++; }
                        result[k] = i < value.Length ? (byte)value[i++] : (byte)'\x20';
                        break;
                    case 'A':
                        while (i < value.Length && !Char.IsLetter(value[i])) { i++; }
                        result[k] = i < value.Length ? (byte)value[i++] : (byte)'\x20';
                        break;
                    case 'N':
                        while (i < value.Length && !Char.IsLetterOrDigit(value[i])) { i++; }
                        result[k] = i < value.Length ? (byte)value[i++] : (byte)'\x20';
                        break;
                    case 'U':
                        while (i < value.Length && !Char.IsLetter(value[i])) { i++; }
                        result[k] = i < value.Length ? (byte)Char.ToUpper(value[i++]) : (byte)'\x20';
                        break;
                    case 'W':
                        while (i < value.Length && !Char.IsLetter(value[i])) { i++; }
                        result[k] = i < value.Length ? (byte)Char.ToLower(value[i++]) : (byte)'\x20';
                        break;
                    case '!':
                        result[k] = i < value.Length ? (byte)Char.ToUpper(value[i++]) : (byte)'\x20'; 
                        break;
                    case 'X':
                        result[k] = i < value.Length ? (byte)value[i++] : (byte)'\x20';
                        break;
                    default:
                        result[k] = (byte)mask[j];
                        break;
                }
            }
            return ASCIIEncoding.ASCII.GetString(result);
        }
    };
}

And the code needed to register and test this one in SQL server:

use myDatabase
go
CREATE ASSEMBLY [SQLMaskApplier]
FROM N'c:\myLocation\bin\Release\SQLMaskApplier.dll'
WITH PERMISSION_SET = SAFE
go
CREATE FUNCTION [dbo].[Transform](@value [nvarchar](1000), @mask [nvarchar](1000))
RETURNS [nvarchar](1000) WITH EXECUTE AS CALLER, RETURNS NULL ON NULL INPUT
AS 
EXTERNAL NAME [SQLMaskApplier].[CBSQLUserDefinedFunctions.Transformer].[Transform]
GO
select dbo.Transform('123456789','999-99-9999')

If you use VS then you do like this:
New project\VC#\SQL server project (add database reference ... - not mandatory but good for automatic deployment and test)
Project Name rightclick and in context menu "Add new item" - select appropriate one SP, Aggregate, UDF ...

and write your UDF, SP ... whatever. VS automatically add a testing code and you can test/debug it using break points:)
Cetin