For those interested in off-the-shelf vocoders that implement the high-compression CELP algorithms, you might be interested in the ZyXEL model U1496E+ modem (about $400) that offers 19.8(and maybe v.fast when specified)/14.4 kbps fax/ CELP (subscribe to comp.dcom.modems for more info). For those interested in the CELP algorithm directly here is some specific directions on getting your own copy: