I noticed that when I browse the web then my IP address belongs to RIM. So it does seem like there is a difference between BlackBerry data and non.
And we suspect that if an application requires APN then it is non Blackberry data. But no one knows for sure!
I have unlimited Blackberry Roaming Data, but this excludes any other data. Still weeks to go before I potentially get a £200 bill as I've been abroad for ages.