Use a Zyxel X550 Router, Fast and Inexpensive!! (Score 1)

I had the same problem, had several Linksys Routers, tried all the 3rd party firmware (except tomato), still choppy VOIP. Installed the Zyxel X-550 and voila, no problems!!! It contains a VERY fast processor. Make sure you install the latest firmware from Zyxel, enable Streamengine (check Auto Classification, Dynamic Fragmentation, and automatic uplink speed), add a "game rule" to forward UDP traffic (ports 5061, 10000-20000) to/from your Vonage box IP address. That's it. Tech For Less has open box units for $33 currently.