I have a situation where AT&T seems to be very uncooperative in their selection of modems (routers) for their business class DSL service. They essentially gave us only two options for modems (which are simply routers) for their service. It seems as though a wide variety of other solutions would work just fine, such as even a DD-WRT flashed device.
It is obvious that they will not support an installation with such a router, however they gave us the impression of doing something like this as being against their terms of service (although they did not explicitly say this; they were more vague saying that they only support X and Y devices that they sell).
The modems (routers) that they sell and support are trash. They do not facilitate any serious port forwarding (I am running SIP video solutions across this connection) and it has become a situation where if I cannot replace their routers, we're going to have to try to find a more flexible ISP (although few, if any, options exist it seems).
Does anyone have any experience working with more robust server infrastructure behind an AT&T ISP connection who has set up their own router solution and can vouch for their "allowing" such a configuration?