could you try "linphone"
[edited] The GPE GUI from linphone-hh package (OZ3.5.4.1) seems to work.
[edited] However, I still haven't manage to record anything via my headset (in headphone jack), neither with arecord nor with the "Record memo" app, independent of alsamixer settings.
When I plug standard headphones, alsa switches the speakers off and Jack to headphones; left/right will play music (via aplay). If I change "Jack" to "Headset" still both left and right will play music. I think this is not the desired behaviour as one of the channels should work as Mic. With the headset plugged, I can listen to music (mono, one earphone), but -- as I said above, I can't use the mic.
Can someone confirm headsets (mono headphone + mono mic) work under OZ on C860?