SPA is a steaming pile of sh!t, although you are right having used high end gateways at our company voip setup, I am snobbish when it comes to that low end hardware; its just full of issues from echo to reliability. In reality it would probably work as an intercom just fine, but I cant bring myself to work with that stuff.
Also, I need 100% reliability where as cheap hardware like that tends to need to be vulcan nerve pinched from time to time. Not good enough...
My dilemma with the camera is it all has to fit into a dual gang box provisioned already, so I need a bullet camera 1/2"->3/4" OD max to shove into the intercom. No ip camera is that small.