Search for an open port (5060 in the example) inside the containers.
vzlist -H -octid | while read CTID; do echo $CTID
vzctl exec $CTID "netstat -antupe|grep :5060"; done
Search for a proccess inside the containers
vzlist -H -octid | while read CTID; do echo $CTID
vzctl exec $CTID "pgrep -lf asterisk"; done