I don't know about Gizmo specific but what are your bandwidth capabilities at the location? I assume you did this with both endpoints on the same LAN. That means you were both going out to the the net and back. Your internet upstream speed is likely the bottle neck. I don't know/think that Gizmo will "reinvite" connections that it finds can go peer to peer so that the video doesn't have to leave the LAN and come back. I did a similar test (SIP) that forced both ends to travel out and back. The quality was good but close to saturating the upstream. With the NITs on different LANs the quality was very good unless WiFI signal was weak. I find the cameras to be optimized for video calls and work rather well.

First I'd check several bandwidth test sites to determine a realistic upstream speed. Many other factors but I'd start there.

jolouis, it must have been a while since you did * in a box. I think *home is now http://www.asterisknow.org/ . Another boxed * is Trixbox http://www.trixbox.org/ . Both of them work very well but not exactly for total newbies if you expect to turn it on like an iPhone... (too bad iPhone doesn't yet have a SIP client..). Easy enough and if you like to learn then they are great tools that work very well with the NITs including video.