So http://www.h323plus.org is an application. Have you (or anyone) tried compiling it?

I must admit that I don't know much about this, other than my quick read of the wikipedia article. Where is the bottleneck that stops it running on the IT? The audio & video codecs presumably?

If you look here: http://en.wikipedia.org/wiki/H.323#Codecs

At least some of the audio codecs are already implemented on the DSP on the tablets. The video codecs include H.263 and H.264 which are both supposed to be implementable (is that a word?!) on the OMAP2420, probably in the IVA, for which we have no code. That's of interest to me, though these codecs can probably be implemented reasonably well on the ARM too.