... not only complaining about things that don't work: Here a success story.
Emil mentioned, that the h263 codec on SC is poorly tested. I use SC for video calling for some time now.
Two of my three contacts I talk to are regularely still on Linphone (my own home, my own Asterisk -so I know it is h263)
H263 comes in two flavours in Asterisk (there might be even more) - I configured the h263-1998 which the *er call h263p. I've had some issues with older Linphones - so on my server only this is allowed.
It works pretty good. OK, one cannot expect crystal clear high res images with that - neither with Linphone, which features some smaller video format - probably QCIF. But for meeting, greeting and keeping in touch it's OK.
So I can say: I've tested H263
Perhaps we can mention interoperability somewhere on the Website as it is a big unique selling point of SC over proprietary offers.