Greetings.

The idea: A client (camera) on the LAN should be able to connect to WAN IPs and WAN IPs should be able to connect to this client through our WAN IP.
The problem: When connected to a WAN IP, they can see/hear us but we can't see/hear them.

Setup: A camera for video conference has its own LAN IP (10.18.16.251). For it to work, the following ports have to be opened; Single - 1720 UDP and TCP, Range - 3230 > 3243 TCP and Range - 3230 > 3285 UDP. For each of these ports I have added a single line in
ip nat inside source static tcp 10.18.16.251 1720 WAN_IP 1720 extendable
and so on.

Additional information:
Router: Cisco 1841
IOS Version is 12.4(7d) IP Base
SDM Version 2.5

Here's some relevant information from the running-config:

!
interface FastEthernet0/0
description $ETH-LAN$
ip address 10.18.16.1 255.255.255.0
ip nbar protocol-discovery
ip nat inside
duplex auto
speed auto
!
interface FastEthernet0/1
description $ETH-WAN$
ip address WAN_IP 255.255.255.248
ip nbar protocol-discovery
ip flow ingress
ip flow egress
ip nat outside
duplex auto
speed auto
!
ip route 0.0.0.0 0.0.0.0 WAN_GATEWAY
!
ip nat inside source list 10 interface FastEthernet0/1 overload
ip nat inside source static tcp 10.18.16.251 1720 WAN_IP 1720 extendable
(the coming rows are all the other ports in either tcp or udp as mentioned earlier in the post)
!
access-list 10 permit 10.18.16.0 0.0.0.255
!

Any help is greatly appreciated.