We provide 4 FXS ports GateWay,
  the model is AG-468. Currently it supports SIP protocol only. It can work with
  most of SIP servers such as Asterisk.

The exciting feature is
  that, it supports T.38 Fax.

You can use it to send or
  receive fax over IP. To learn more information about this product, please visit:
 

http://www.unifycall.comhttp://www.unifycall.com">http://www.unifycall.com>

http://www.unifycall.com/index.php?main_page=product_info&products_id=194