The reason mmc838 is required is that with the introduction of mps in 4.4x the manual setting of private or public for spnet and ip phones was removed. Now the system assumes if you have private with public turned on anything not in the local subnet of the mp card has to go through public.
Mmc838 lets you over ride this.
Just put x.x.x.255 (eg 192.168.1.255) to cover all ip addresses in the remote network.