Some of these setups require a specific firmware version or a tweak setting I don't know about.
Try the latest firmware and if that doesn't work, make the call to the support line.
I have a Linksys BEFSX41 Router connected to a Cisco ATA186. I use this for my VoIP calls. While I am able to make and receive calls using my VoIP phone, I get cut off exactly after 5 minutes (300 seconds of talk).
I have tried changing the idle time in teh Linksys setup to beyond 5 minutes, but it still does not work.
I get cut off after 5 minutes.
Any suggestion to overcome this problem.