On my setup just to be sure, I configured each of my SIP phones and ATA's to use different SIP and RTP ports. I have the Linksys from VOIPo which I believe uses 5060 and 5061. I also have a Cisco ATA186 that I set to use 5066, and a Grandstream that uses 5101. My Polycom uses something like 5068. The RTP ports are usually above 16000 and sometimes are random depending on the device, but I set them differently if I can.
Scott