An Alternative To QoS In The Router
What if you can't or simply don't want to replace your router? There are other options. Both D-Link and Hawking Technology (amongst others) make "voip accelerator" devices that are designed to add QoS to a network that otherwise lacks such capability. (Hawking's HBB1 is reviewed here). Both of these devices are installed between the existing router and the rest of the users network. All traffic passes through the device, which can thus identify RTP streams and prioritize traffic accordingly.
There are threads on the Vonage users forums that would indicate that these devices really do help some people with QoS issues. YMMV.
Recommending A Router
There are about three short of a zillion low cost consumer routers available. It is not my intention to make specific recommendations about hardware routers. Instead I'd rather convey my experience with those that I have actually used.
However, I will make one exception to this. If you are interested in learning about routers, feel like supporting an open source project, and cost is not your major concern, then I suggest you consider m0n0wall.
Addendum: I just happened to learn that the Linksys BEFSR-41 v4 router does in fact have a QoS feature like the BEFSR-81 that is the basis of much of this article. Apparently this become possible in the v4 hardware revision.
In the second and final part, I'll look at Traffic Shaping and Power Considerations.