C# regex to filter a phone number

1:  using System; 
2:  using System.Collections.Generic; 
3:  using System.Text; 
4:  using System.Text.RegularExpressions; 
5:   
6:  namespace ConsoleApplication1 
7:  { 
8:    public class PhonenumberFilter 
9:    { 
10:      public bool IsNumberOK(string num) 
11:      { 
12:        //this pattern is to match all phone numbers, except a number starting with 15. 
13:        //the pattern tries to match any of the valid number ranges: 0....-09.... and 10...-14... and 16...->169..... 
14:        //min length = 5, max length = 11 
15:        string pattern = "^(0[0-9]{4,10}|1[0-4][0-9]{3,9}|1[6-9][0-9]{3,9}|[2-9][0-9]{4,10})$"; 
16:        Regex reg = new Regex(pattern, RegexOptions.None); 
17:   
18:        return reg.IsMatch(num); 
19:      } 
20:    } 
21:  } 
22: