My TA824 is set up as a key system. I have 4 lines and I direct select each line, or know which line I'm using. The idea that you dial "9" for an outside line and get echoes, or actually as you said, it's incoming andyou flash and it goes away, didn't tell me that you hear the echoes on lines 6-8 vs. 1-3. If you hear an echo on line 2 and use line 2 to call out (logical option) doesn't seem that it would be the fault of the phone system. Remember, you have the CLOSED end of the network. Nothing changes.

Carl