VOIP Software Added to My Website

I need someone to add a high-quality VOIP system of some sort to my online English lessons website so that teachers and students ca nhave voice communication. Ideally, this would be connected to a whiteboard facility so that the tutor can write words etc. for the student. I have tried most, but the sound quality is always not good enough or not consistent. It must have a stable and high-quality sound and needs to have no downloads required by the students using it. I would prefer it if the whiteboard didn't use flash technology, but I don't know if this is possible.