But it would be comforting if I could find someone who has actually done this with success. I'm not sure I can go back to the factory firmware once I've flashed the new stuff.
By the way, I realize that a new N router with built-in QoS would solve this problem, but if I were made of money I wouldn't need to use Ooma.
Having said all this, it's not that big of a deal once you do it. Just carefully follow ALL of their suggestions. READ THE FORUM PAGE FOR YOUR ROUTER.
I have tested DD-WRT on a Cisco Linksys WRT-160Nv3 and a Cisco Linksys E2000. It did not perform well on either, where as QoS with the Factory firmware on both those routers performs excellent. So, the short answer is you will have to just try it. If it doesn't perform well, then I would recommend getting a Cisco Linksys router while their still available. Good ones are E2000, E3000 and E4200. If you're not looking for high performance and just need good QoS, then you can use an older WRT as the ethernet gateway with QoS from your ISP modem and feed the Buffalo for WiFi to the rest of your network. This is what I do. Look at my signature and you'll see the order I have my ISP modem and routers connected. My E2000 handles the QoS and IP address assignment for the rest of my network.
Service: Premier 1/30/2012
BELL Canada Port: 1/30/12 - 2/13/12
TekSavvy via BELL FTTN: 25 Mbps/10 Mbps
Setup: Sagemcom 2864 > Cisco E2000 > Time Capsule v1 > Telo
Handsets: Panasonic KX-TG6655S DECT 6.0
I've configured QoS and it works fine for me. I tested it by uploading a large file to a remote web server, from a PC also attached to the router, while making a phone call with the Ooma system. Without QoS configured, the conversation received on the other end was very choppy and with delays of up to several seconds. With QoS enabled the conversation was fine in both directions (but, of course, the file upload slowed to a crawl until the phone call ended).
Also note that my internet service only provides an upload speed of 256Mbps, which is actually below what Ooma recommends.
Ooma has a static address with qos set for highest priority.
I had to play around with the upload number a little.
On this router, Tomato works better than the stock firmware. Never tried DD-WRT.
Ooma is the most stable it's ever been with this setup.