C# 手机号分隔显示

 public static string ReturnPhoneNO(string phoneNo)
 {
      Regex re = new Regex("(\d{3})(\d{4})(\d{4})", RegexOptions.None);
      phoneNo = re.Replace(phoneNo, "$1 $2 $3");
      return phoneNo;
　　　 //如果手机号为15090734419   则return: 185 7181 5021
 }