Altigen Ip Phone Nat Support Feature - Altigen AltiContact Manager Version 5.0A Administration Manual

Setting up H.323 Traffic Forwarding for NAT
Enable the H.323 Cross NAT Support Enable check box and then enter
the NAT router's public IP address in the NAT Mapped Public Address
field. If you have the local IP phone, which is in the same private network
with AltiWare, enable the Use Private Address in Private Network check
box; then enter the Subnet Address and Subnet Mask of the private
network.

AltiGen IP Phone NAT Support Feature

When the AltiGen IP phone (firmware version 1116 or above) is running in
normal mode and registered to the server (AltiWare version 4.6 SP1 or
above), the phone has the intelligence to support H.323 cross NAT. But the
NAT that is in front of the AltiGen IP phone must be set up according to
"Setting up H.323 Traffic Forwarding for NAT" on page 9-28.
9-30 AltiContact Manager Administration Manual