Recently, I talked about how some ISPs tend to block SIP traffic. If you have a branch office that does block SIP traffic, then you have the logical option to change the SIP port on your devices. This however, is not always feasible. Next best thing would be, if you have a VPN between the branch office and main office, to create static routes in your routers to route all SIP traffic over the VPN tunnel.

You’ll notice ISPs blocking SIP calls usually do this by blocking SIP port 5060 so if you change the port on your phone system to something else, and configure your end nodes to use the new port, they will work. This traffic will be visible to your ISP though, so the better option will be instead of changing ports to just route SIP traffic over you VPN.

Always check your local laws as I am no lawyer so any ideas you try, you are doing at your own risk.

I can’t believe ISPs are actually thinking they can hold the flood back by simply blocking SIP port, such ISPs are truly grasping at straws to keep their ancient model in the market.