Random SIP ports instead of 5060?

Is there a compelling reason for NOT using random SIP ports on SIP phones?

We’re running an Asterisk 1.8 server providing pro bono services to a non-profit public service agency located a few towns away. They have a Grandstream GSW4108 FXO gateway, and about a dozen or so Grandstream phones that are behind a NAT firewall.

I set each of the phones to use a different port number… 5060/5062, then 5064/5066, etc… in the hope that I could restrict the firewall on this end as much as possible while still allowing all PBX traffic. But, then I discovered that their Comcast router changes port numbers half the time anyway, so it seems kind of a useless exercise to go through the additional effort to keep the ports separate on each phone… could just as well set them all to use random ports and forget it.

So, is there a reason, that I’m not considering, why I should not do that?

Thanks…

Eric / www.rkt-tech.com