It varies. In those countries that have a domestic premium rate (1-900) market, the surfer pays more - but you recieve more.
In those markets that do NOT have such numbers, we 'export' the call to an overseas carrier with whom we have a revshare agreement. So the caller makes a regular international call, costs of these vary enourmously (carrier, priceplan etc). Some are even using Skypeout to get their passwords!
Your payouts are fixed, see
http://www.password-by-phone.com/revenue.php