Is VoIP supported?

Yes, Coccinella supports Voice over IP using Jingle. The Speex codec is used by default. Coccinella uses the iaxclient library for internet telephony.

Is video conferencing supported?

No, video conferencing is not yet supported.

Is Coccinella's VoIP compatible with Google Talk?

No, currently Coccinella only supports IAX, which is not (yet) supported by Google Talk. So, you cannot yet receive calls from or make a call to people using the Google Talk client.