I know this is almost a year old, but I am still having a problem rebooting Grandstream GSX280 and GXP2010.
While searching I located a perl script here http://www.pkts.ca/gsutil.shtml which helped me and I hope will help anyone reading this wishing to remote reboot Grandstream phones.
This works and will work on several phones from one command line.
Can this be incorporated into the OSS Endpoint Manager to reboot these phones?