title: iphone sdk - Remove all characters except for numbers 0-9 from a string
body: <p>OK So here's the plan. The XML I'm getting data from allows non-numeric text in phone number fields (for descriptions or contact names, etc). I am trying to extract only the numbers and call the tel: URL with them to initiate a call. Here's whats NOT working:</p>
  
  <pre><code>NSCharacterSet *charset = [[NSCharacterSet decimalDigitCharacterSet] invertedSet];
  NSString *number = @"(555) 555-5555 Office";
  NSString *strippedNumber = [number stringByTrimmingCharactersInSet:charset];
  NSString *phoneURL = [NSString stringWithFormat:@"tel:%@", strippedNumber];
  [[UIApplication sharedApplication] openURL:[NSURL URLWithString:phoneURL]];
  </code></pre>
  
  <p>if there are any obvious typos, they're just typos. :)</p>