On a related note, it's pretty painful to debug what exactly going on with these headless devices. This is not just a Grandstream device issue. I face the same issue with the Linksys PAP2. Grandstream did provide logging to an external server which helped me quite a bit. However, I need either a hub or a low-end switch that can do span. I do have a Linksys WRT54G, I can put openwrt firmware and do tcpdump right on the box. That's a project for another day.
Incidentally the Grandstream box appears to be running Linux though Grandstream website makes no mention of it. I'd love to get a shell prompt on it. It's a very small and sleek device.