Asterisk will be running in the background, but it consumes a great deal of the computer’s resources as i runs. Especially if you are using zaptel cards, you will notice that running X can impact performance dramatically. Some have few problems with it. If you really want asterisk to keep running reliably, you can get away with a much cheaper machine and dedicate it to the task
http://fonality.com/trixbox/forums/trixbox-forums/open-discussion/there-gui-centos
