connecting Vonage to ATT Uverse?

It sounds like there could be a 'Router behind Router' network configuration issue.

RBR occurs when you plug in a router into another router and both routers end up routing traffic on the network. This can cause various conflicts and abnormal behavior such as what you are describing.

When you plug-in the Vonage adapter to the Uverse [2-Wire] Router, the Uverse Router detects that the Vonage adapter is (effectively a) Router and then starts to assume the Vonage Router should be treated like the primary router.

What happens then is that all the traffic in the network that goes to the Uverse Router is then redirected to the Vonage Router (because it thinks the Vonage adapter should be routing the traffic instead). The Vonage Router does the only thing it can do and sends the traffic back to the Uverse Router with a virtual note saying I'm done routing and the traffic should go out to the Internet now.

So imagine being on a road and you reach an intersection (Router). You want to go straight, but there is a sign blocking the road saying you must detour by turning left. After you turn left you arrive at another intersection and there is another sign blocking the road, but this time it says you must make a U-Turn and go back to the first intersection. After you make the U-Tun you and go back, you can then turn left and continue down the road that you wanted to go down originally. This is effectively what's happening.

The problem here is not just that traffic is being unnecessarily detoured, but that QoS is also being stripped.

QoS is a mechanism which is used to prioritize traffic over other traffic. For instance, we can say that TV should have priority over email. Thus, it is not possible for email to interfere with the TV traffic because the TV will always be given 'right of way' at the 'intersection' (router) and the email traffic must wait patiently (for a few microseconds) until there is room (bandwidth) available for it to go through.

Imagine that QoS is a special pass which lets you drive in the express lane, and if you don't have the pass, you must drive on the regular busy road with everyone else. Now imagine arriving at the intersection in the scenario above and having to go through the detour. Now picture yourself arriving at the second Intersection and meeting a police officer. The officer says to you, 'give me your QoS pass to continue'. You must continue, so you have no choice but to give the officer your pass. Now you can continue to your destination, but you no longer have your pass and you must drive on the busy road with all the other cars.

That is what is happening with your TV service. The TV cars usually have a QoS express pass, but they are being stripped of the pass when they go through the detour through the Vonage adapter, so when they come out of the detour they are stuck in traffic on the busy road and ultimately the TV service cannot be delivered in time and the picture/audio freezes.

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How do you correct this problem?

Try turning off both the Uverse Router and the Vonage adapter. Now plug-in the Vonage adapter (and be sure it is connected to the Uverse Router. After a few moments, plug-in/power-on the Uverse Router. If all goes well, the Uverse 2-Wire modem will detect the Vonage adapter as a standard network device rather than a Router, and there shouldn't be an RBR problems. The issue typically occurs when you plug the Vonage adapter in after the Uverse Router is already on and then the Uverse Router starts trying to give the Vonage adapter routing duties.

If this does not correct the problem, you may have to put the Vonage adapter in DMZ mode. This over-rides the 2Wire's RBR detection feature and among other things it may actually help improve call quality. You must refer to your operating manual or contact AT&T to find out to configure the Router to put the Vonage adapter on a DMZ because the instructions are too complicated to explain here.

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The other guy (Ben) gave you a very technical answer so it may confuse you although he is quite correct in what he said. Let me try to give you an answer in laymen term. I assume that you connect the Vonage adapter to the cable box (internet) and then the AT&T router sits in the middle between the Vonage adapter and the TV. So first power down both Vonage adapter and AT&T router. Then power up the Vonage adapter first and wait a few minutes for the messages on the LED that say that the connection is successful. Then power up the AT&T router. It should then negotiate with the Vonage adapter for addresses and then everything should work afterward.