I have a AVAYA Partner ACS R7.0 with 10 analog lines on 20 extentions.
One one of the phones lost dial tone on one of the lines after they press some buttons ( which they cannot remember ).
The line that is dead works on all of the other phones, so it isn't a problem with the analog line. I also replaced the phone with another workers phone and problem remained. It must be some kind of programming on the ext. but do not know what.