Where to put the ATA depends on your internet connection and your preferences. If internet performance tanks every time you're on the phone, you'll probably want the ATA behind your home router but with good QoS priority (and most likely, ports forwarded). If you don't notice any problems with using the internet the way you want to use it, even with your ATA "outside" your home router, there's no harm in leaving it that way. You may even prefer to have it that way to simplify troubleshooting of the VoIP line (if there are problems) and to avoid setting up QoS and/or calls sounding wonky if your internet use spikes (e.g., gaming or if you initiate a large upload).