The Sipura SPA-3000.
An interesting factoid is that even though the Sipura SPA-3000 supports up to 3 active calls, the fine print notes that it only supports one G.729 call. Presumably this is because G.729 requires patent-related license fees.
After months of nervousness and procrastination our main phone line is now VoIP. I have connected our DECT handsets to the Sipura SPA 3000 which SIPs into my Asterisk box using G.711u. Asterisk is using G.726 to OzTel with an IAX2 trunk and the sound quality is good. I plan to do some monitoring and look at delay and jitter (if available). Pulling the Ethernet from the SPA 3000, or shutting down Asterisk on my BSD box makes the SPA 3000 fail-over to direct PSTN dialing within seconds.
So far, so good.