I agree with newtecky. If it is not that, you may want to try another router (even though you stated that you tried others), I have never had a single problem with an off-the-shelf TrendNet router (usually a wireless per customer request).

https://www.trendnet.com/products/

They seem to be the only consistent "no problem" router with the IP Phones.

Also, who is the provider?


- Tony
Ohio Data LLC
Phone systems, data networks, firewalls and servers in Central Ohio.
Some people aren't used to an environment where excellence is expected.