Rick Collins wrote in a message to David Bowerman:
db> Going by the standard AT command set, ATF1 would turn on-line
db> echo off (full duplex mode) while ATF0 should enable on line
db> echo -- when a character is sent to the modem, it is echoed back
db> to your system as well as being sent to the remote system. 
 RC> I believe you mean E1 and E0.
 RC> :-)
Nope.  E1 and E0 control echoing characters back in command mode before the 
connection is made while  F1 and F0 control echoing the characters back in 
on-line mode after the connection is made.  If it was good enough for a 
SmartModem 300... ;-))
Regards,
       David
--- timEd/2 1.10+
---------------