Just to be clear: making portaudio clocking to be more efficient not only will lower portaudio itself to use less cpu, but will lower the cpu usage of the skype clients, and probably of freeswitch too, because there will be less taxing on the timers at the kernel level, and so all applications will have less contention, less blocking, etc.

Anyway, the only way we have to lower cpu usage is to act on portaudio (that is used uniquely as a source of timing by skype client, eg: its reads and writes on portaudio are moving blank samples, just to clocking the reads and writes on TCP socket of the real audio packets). Portaudio uses realtime kernel timers from userland, and is not optimized at all for using many of them concurrently.

That is the only moving wheel we can modify. We cannot modify the Skype client itself (unfortunately :) ).