I have an SPA3000 ATA connected to a WRT54G (firmware 3.3.6). I have a strange problem that I'm hoping someone may be able to shed some light on. The SPA uses UDP port 5060 for an outgoing SIP connection to an Internet server. However, the SIP Registration does not get a reply from the server (packet capture between SPA and WRT54G shows this). If the WRT54G is set to port forward 5060 to the SPA, the Registration works fine and reply packet is seen. While testing, I tried setting the SPA's SIP port to 15060 and the Registration works without a port forward being set up - there is a reply from the server (seen in a packet capture). It seems like the WRT54G is doing something peculiar with port 5060 (BTW, 5061 has the same problem) that it isn't doing with port 15060. Any suggestions? I know I have a workaround, but I'm just curious why the different behaviour.