Some Frquently Used Extension Methods

Here I am going to post some of Frequently used extension methods which can be used with a string variable

/// <summary>
        /// It formats strings into a name format.
        /// </summary>
        /// <param name="firstname"></param>
        /// <param name="middlename"></param>
        /// <param name="lastname"></param>
        /// <returns></returns>
        public static String ToName(this String firstname, string middlename, string lastname)
        {
 
            if (!string.IsNullOrEmpty(lastname))
            {
                return String.Format("{0} {1} {2}", firstname, middlename, lastname);
            }
            else
            {
                return firstname;
            }
        }

 /// <summary>
        /// It formats string into a phone format
        /// </summary>
        /// <param name="phonenumber"></param>
        /// <returns></returns>
        public static string ToPhone(this string phonenumber)
        {
            if (phonenumber == null || phonenumber.Length == 0) return null;
            long pn =
                long.Parse(
                    phonenumber.Replace(" ", string.Empty).Replace(",", string.Empty).Replace("(", string.Empty).Replace
                        (")", string.Empty).Replace("-", string.Empty));
            if (pn == 0)
            {
                return string.Empty;
            }
            else if (pn.ToString().Length == 10)
            {
                return String.Format("{0:(000) 000-0000}", pn);
            }
            else if (pn.ToString().Length == 7)
            {
                return String.Format("{0:000-0000}", pn);
            }
            else
            {
                return string.Empty;
            }
        }

/// <summary>
        /// It formats a string into SSN
        /// </summary>
        /// <param name="ssn"></param>
        /// <returns></returns>
        public static string ToSSN(this string ssn)
        {
            if (ssn == null || ssn.Length == 0) return null;
            long data =
                long.Parse(
                    ssn.Replace(" ", string.Empty).Replace(",", string.Empty).Replace("(", string.Empty).Replace(")",
                                                                                                                 string.
                                                                                                                     Empty)
                        .Replace("-", string.Empty));
            return String.Format("{0:000-00-0000}", data);
        } 

 public static bool IsValidDate(this string inStr)
        {
            bool isValidDate = false;
 
            if (inStr != null)
            {
                isValidDate = inStr.Trim().Length > 0;
                DateTime dt;
                if (isValidDate)
                {
                    isValidDate = DateTime.TryParse(inStr,out dt);
                }
            }
 
            return isValidDate;
        }

 public static string ToZipCode(this string instr)
        {
            if (instr != null)
            {
                instr = instr.PadRight(9, '0');
                return instr.Substring(0, 5) + "-" + instr.Substring(5, 4);
            }
            return string.Empty;
        }

 /// <summary>
        /// It formats string into ToCurrency.
        /// </summary>
        /// <param name="inStr"></param>
        /// <returns></returns>
        public static string ToCurrency(this Decimal inStr)
        {
            return String.Format(System.Globalization.CultureInfo.CreateSpecificCulture("en-us"),"{0:C}", inStr);
        }