P.S. I forgot to mention; some ATA's also have a built in router. Therefor, in that case, it is totally feasible to put that type of ata directly after the DSL or cable modem (WAN) and put your network router after it. You still have a double NAT situation, but that is something you can work around. If all you have are PC's and other basic network equipment, it's not a big problem. Double NAT can be an issue for servers, voip, and a few other things.

Bottom line; I prefer to put the ATA after the network router. I prefer to port forward IF NECESSARY. You don't know if it's necessary until you try. It depends on the router and service you have. My last router, I had to do port forwarding. The new router I have now, I don't have to forward anything.