Another happy user of those blue boxes.
I have several of those, and never could get much info about what the units could do or not do.
Seems like there are a ton of options, but as far as I know ,nobody knows the full extent of those settings.
I do not think that a gatekeeper will help, the function of the gatekeeper is mainly to keep track of those pesky, moving I.P. addresses when you have ADSL or a cheapy provider that keeps changing I.P. ‘s every few hours.