I keep thinking that so many items are deeply embedded within the OS.
We heard a bit about this with the browser and being to share webpages directly from within the browser. I bet video calling will be the same way. You have a contact and are able to choose whether you call with BBM video, Skype, or ooVoo. You let the USER decide how they wish to contact that person because they have all the information they need to decide how to contact them.
What I'm thinking/envisaging is that your contacts contain all the data for skype, oovoo, etc. so that you can choose which way you contact with them. This allows you to not have to go into an app to find that contact. You find the contact and then you choose how you want to contact them because you know on which system (bbm video, skype, ooVoo) they are online. To me, that maintains a beautiful way to flow.
I think this is why they made sure to push the 'invoke on' framework.
If my vision is true, this will really improve (and differentiate the BB10 experience from other OSes). Why go into another app only to find out that the person isn't online there??