The only thing I can think of is to use something like"http://www.dyndns.org/cgi-bin/check_ip.cgi「others may have a be」

NSUInteger  an_Integer;
NSArray* ipItemsArray;
NSString*externalIP;

NSURL *iPURL =[NSURL URLWithString:@"http://www.dyndns.org/cgi-bin/check_ip.cgi"];

if(iPURL){
    NSError*error = nil;
    NSString*theIpHtml =[NSString stringWithContentsOfURL:iPURL 
                                                  encoding:NSUTF8StringEncoding 
                                                     error:&error];
    if(!error){
                NSScanner*theScanner;
        NSString*text = nil;

        theScanner =[NSScanner scannerWithString:theIpHtml];

        while([theScanner isAtEnd]== NO){

                // find start of tag
            [theScanner scanUpToString:@"<" intoString:NULL]; 

                // find end of tag
            [theScanner scanUpToString:@">" intoString:&text];

                // replace the found tag with a space
                //(you can filter multi-spaces out later if you wish)
            theIpHtml =[theIpHtml stringByReplacingOccurrencesOfString:
                    [NSString stringWithFormat:@"%@>", text]
                                                   withString:@" "];
            ipItemsArray =[theIpHtml  componentsSeparatedByString:@" "];
            an_Integer=[ipItemsArray indexOfObject:@"Address:"];

                externalIP =[ipItemsArray objectAtIndex:  ++an_Integer];



        } 


            NSLog(@"%@",externalIP);
    }else{
        NSLog(@"Oops... g %d, %@", 
              [error code], 
              [error localizedDescription]);
    }
}




[pool drain];
return0;