SEO / USER friendly urls won't work.

Hi there,

I am trying to figure out why our website www.webuyback.com.au won't display User friendly / Seo friendly URL's .

I am pasting the URL title code from url_helper.php file down here

if ( ! function_exists('url_title'))
{
function url_title($str, $separator = '-', $lowercase = FALSE)
{
if ($separator == 'dash')
{
$separator = '-';
}
else if ($separator == 'underscore')
{
$separator = '_';
}

$q_separator = preg_quote($separator);

$trans = array(
'&.+?;' => '',
'[^a-z0-9 _-]' => '',
'\s+' => $separator,
'('.$q_separator.')+' => $separator
);

$str = strip_tags($str);

foreach ($trans as $key => $val)
{
$str = preg_replace("#".$key."#i", $val, $str);
}

if ($lowercase === TRUE)
{
$str = strtolower($str);
}

return trim($str, $separator);
}
}


Still whenever I create aproduct, the url looks like this : http://www.webuyback.com.au/sell_your_phone/159

Any help would be highly appreciated.