You're right, busybox doesn't support the array syntax in your script.
In order to set the values, you might use
eval ipValues$count=$(echo $LINE | awk -F'=' '{print $2}')
and to read the variables
ifconfig eth0 ${ipValues0} netmask ${ipValues1}
echo "IP :: ${ipValues0} SUBNET MASK :: ${ipValues1}"
route add default gw ${ipValues2}
echo "Default Gateway :: ${ipValues2}"