I have two gateways setup like this: http://pastebin.com/m41092fa6 I have two dialplans setup as follows: http://pastebin.com/mde96a74 Everything works fine for the first provider, but the second provider drops calls after about 30 seconds. I've been told it's a NAT issue, but would only one provider be dropping calls ? If re-registration is interrupting calls I would have thought it would do it on both providers. It was suggested that I configure one gateway to use a different port and I've tried setting the port like this: <param name="realm" value="sip.pennytel.com:50601"/> But I can't get it to register. I've tried connecting my softphone (X- Lite) directly to either provider by specifying the hostname as sip.providername.com:5061 and it can't register either. Is this the correct way to specify a SIP port to use or is it just that my provider doesn't listen on any other ports than 5060 ? When I specify sip.pennytel.com:5060 it still registers fine. Is this the best way to solve my problem ? By using an alternate SIP port ? Or is there likely to be any other reason why calls are dropping out ?