I have an incoming POTS line connection to an FXO port on a 1760 gateway. This POTS line is only providing -24 voltage rather than the normal -48 voltage. This seems to be preventing the FXO interface on the router from sending DTMF that is acceptable to the POTS line. I have read that I need to change the FXO line in use voltage on the gateway to a lower value in order to allow DTMF to pass correctly to the POTS line. Does anyone know how to change the FXO line in use voltage, or know if it is possible to convert the -24 to -48 between the FXO port and POTS line?