Someone on dslreports.com years ago reverse engenered and worked out the format of the config. file and created a config file creator program as well as a serial script to hook to its TTL serial port to change the address of the TFTP server. I now have it providing two analog lines from voip.ms that have a strong enough REN to power several old analog phones with real bells in the house.
It even allows you to pulse dial class five codes like disable call waiting and call voice mail. EX. 1,1,6,9 = *69 if touch tone dialing.