I've had my ATA in the DMZ since day one and haven't set up any port forwarding for it. I set up a DHCP reservation, based on the ATA's MAC address, for a specific IP address and use that IP address to put the ATA in the DMZ.

My router's firmware, a DD-WRT version, only allows a single device in the DMZ so if I had a second device come along that required the DMZ too, I would have to reconfigure something. Haven't run into that yet.