I'm just beginning to read about Asterisk implementations, and so far the Raspberry PI is attractive. However, I see on the OPEN-WRT site that there is an Asterisk package that seems suited for installation directly to a node. I haven't looked to see if it's in the package repository for BBHN yet.

So, has anyone tried to implement an Asterisk PBX on a node, and succeeded? Is it practical, or is the Raspberry PI a better approach?

Seems a lot to ask of a little System on a Chip (Brain on a Stick?) but it could be interesting.

Yes. I originally did it on the node (I still do). You can find the discussion under the VoIP thread: http://hsmm-mesh.org/hsmm-mesh-forums/view-postlist/forum-9-voip/topic-284-asterisk-running-natively-on-hsmm-mesh-node.html
Please read through the whole 2 pages worth of discussion.  In the document attached in the last post, you can skip over step 1 in "Configuring the VoIP phone."

Seems a lot to ask of a little System on a Chip (Brain on a Stick?) but it could be interesting.
It works fine. I've sustained multiple 2+ hour phone calls without experiencing a degradation in audio and node performance.