asterisk users - Jun 2005 - Multiple phones on a Zap FXS extension

Hi
	I have Asterisk up and running perfect with a Digium TDM400P card and 4
FXS ports. There are 4 AT&T 4-Line 954 phones hooked to the system Each
of the 4 lines is hooked to each phone. The problem is when you are on
line 1 (or any line) and someone else picks up line 1 they can here the
conversation. When the phone are hooked to the PSTN in the same way line
1 will be lite up to show that it is in use and you cannot join the call
without pressing a certain key sequence. How can I get the phones to act
like they do when they are connected to the PSTN when hooked to the
Asterisk server.

Any help is appreciated.

Kelly