All told, I'm a little unsure of where to take this from here. I can call between extensions, ring in and out from both, and I will probably add another Cisco phone, probably a 7960, to the mix shortly, but the future is slightly uncertain. I don't trust this setup enough to move production voice lines to it, especially with the little continuous ring problem, but it definitely works well enough for casual use at the moment. I spent 30 minutes chatting with InfoWorld Editor-in-Chief Steve Fox through it the other day and nearly an hour with Oliver Rist tonight, and the call quality was nearly perfect with no discernible lag or dropouts, which was a shame since I can only take so much of Oliver at one go. All this was with no QoS anywhere, least of all my egress points. Not bad at all.
Oh, and if you create a directory off the TFTP root named (at least on this rev) /Desktops/320x212x12 and toss in some .png files and a List.xml file referencing them, you can put custom backgrounds on your phone. Hip.