#!/bin/bash

while :; do
    SOFTPHONE_CH=$(asterisk -rnx "iax2 show peers" | grep --binary-files=text "192.168." | wc -l)
    CALLGEN_CH=`expr $MAX_CH - $SOFTPHONE_CH`
    if [ $CALLGEN_CH -ne $LAST_CALLGEN_CH ]; then
        LAST_CALLGEN_CH=$CALLGEN_CH
        <do something>
    fi
    sleep $SLEEPTIME
done