I think I understand....
Please correct me if I'm wrong.
You have an analog station port connected to a page system that sends out dial tone over the PA after the user hangs up.
Here's my first guess at this. Rather than sending out a #, program the analog port connected to it to be a "non-busy" extension. No more dial tone. You'll have to go through the help docs for the "how-to" but it should be pretty simple.
A "non-busy" extension never gives out dial tone and can't dial anywhere. Originally designed to be an emergency type extension, if it is in use, the next call automatically barges in. Therefore *non-Busy*.
Ralph