if it works crystal clear with ip phones internal than id say cards and programming are all ok...
I am not a big fan of those shared T1 circuits... that is probably where your problem resides,
I bet if you got a cable modem with static ip dedicated to the cix phones only you would be ok
you shouldnt be so quick to crucify your dealer when the problem has to do with the internet and the type of circuit coming in, and not the system
