BBM Calls / Video Calls go through BIS?

I know there are many threads talking about BIS and BB10, but before writing this post I've read "nearly" all of them and haven't found the answer.

It is an easy question I think:

When I use BBM calls / video calls I'm using BIS or I'm using "normal" 3G from my data plan?

I would explain a little bit why I ask this. Now that there is no more BIS service for BB10 I do not have an unlimited plan so when I reach the 1GB they send me an sms saying that my speed is reduced. (I would say to a ridiculous levels, I can't even surf the web with that speed!).

So that is why I made this question, because it would be great to know if I'm using my data plan or I'm using BIS (which, here in Spain is unlimited).

Thanks for your answers guys!

Cheers from Barcelona. ;)