The Electronic Serial Number Module enables older modems (PTC-II and PTC-IIe) to be upgraded with PACTOR III mode firmware.  PLEASE NOTE: this is a hardware modification and requires your modem to be returned to Farallon Electronics . 

The $119.00 price is inclusive of the ESN Module (hardware) and labor but does not include the PACTOR III license, which must be purchased separately.  Please contact Farallon for clarification if needed.

The PTC-II and many PTC-IIe modems pre-date the Electronic Serial Number system that is embedded in current production PTC modems.