Chances are, the "WAN", was a DSL type of modem, which was also a router itself. Therefor, your ATA was actually behind a router. Many people do "Double NAT" (Use 2 routers) and don't always even know it. Many cable modems, tend to be just modems. Unless you get one that is also a router and wifi.

The thing is, the only way you can put an ATA between a true WAN modem (Meaning it doesn't have a router built in), is if the ATA is also a router. If it wasn't, then none of your home PC's could work on the internet, because they wouldn't have an IP address. See, what a router does, is bring 2 (or more) networks together. E.g. your home network and the your internet provider/internet. Your router normally takes the 1 IP address you get from your ISP, and using NAT, it makes a bunch of private IP addresses. All those 192.168.1.x types. That's how more than one device can be on the internet at the same time, even though you only have 1 IP address from your ISP.

So what you were reading about putting the ata between the WAN and the home router, was probably because that particular ATA also had a router built into it. If it didn't, your home network would not have worked. The normal is after your home router. Unless you have a combination DSL/Cable Modem/Router/WIFI and you don't have a separate router. Again, not uncommon. So, to answer your question, no, it was not in the DMZ being before your router, because the DSL/Cable (Modem/Router) provided NAT and was providing the ATA a 192.x.x.x type IP address.

All DMZ does, is open up ALL PORTS for an specific IP address. My setup, I don't do ANY port forwarding, and everything works perfectly fine. Then again, on my old router, (I usually buy a new router ever couple years because I'm a technogeek who likes new toys), that old router I did forward ports for the ATA. But the first thing I do is try no port forwarding, no dmz, and SIP ALG, and see how it works. My current modem was designed specifically for gaming/voip and many QOS priority type applications. So maybe that's why I do so well without anything forwarded or DMZ.

For what it's worth, I have one of the original ATA (Linksys PAP2) that I got from VoipO in like 2007 or 2008. But, I also have an IP PHONE, that doesn't use an ATA and is plugged straight into my network switch just like it was a PC. I also have a softphone app on my android cell phone and a software softphone on my laptop. I go on the road a lot, and some places actually have internet with almost no cell service. I use the app and softphone to call my wife. The IP phone on my network..... well, that's just another toy. Plus, if the ATA was to ever break, I'd still have at least one good working phone. Take care..... Mike.....