Router: WRT54GL (DD-WRT v24 preSP2 build 13064)
ATA: RT31P2
ISP: Comcast (12/2)

Cable Modem -> WRT54GL -> RT31P2

Ever since setting things up this way:
http://forums.voipo.com/showthread.php?t=1919

I haven't noticed the phone being down (Phone 1 always lit). My wife uses the phone probably 200-300 mins per day and hasn't complained once since this setup. In previous configs, the ATA would lose reauth randomly. And trust me, she lets me know every single time something bad happens.

I'm going to try to put Tomato back on the WRT54GL in the above configuration to see if it still works, as I prefer it over DD-WRT.

-Craig