System overview   
1.44  EST3 Installation and Service Manual 
is low cost, as multiple remote telephone jacks can be installed 
on a single branch circuit. 
The main disadvantage of this method are: that five phones may 
not be adequate to properly cover the facility; a circuit failure 
can render many of the phone jacks useless; the location of the 
incoming caller is not precisely known; and troubleshooting is 
more difficult.