Not sure if all Blackberrys do, but my 9900 has the facility to create a 3G hotspot, no app involved, just switch the hotspot on in the connection setting page. I can connect my iPad too it, or my Playbook when out and about. Pretty sure all half decent 3G smartphones these days will do the same.
Or if you have a BB phone, use BB Bridge, which basically joins the two devices together. Documents, emails etc shared across both devices.
What I mean about size is that 10" tablets are just a little too large to be truly portable. Great for using in the house, but a tad too big for a pocket or (in my wife's case) handbag. Blackberry/Nexus is a better size, fits in a jacket pocket, for example,but the keyboard is more difficult to use (but only a bit). I've not owned a 8" tablet but I suspect they might be the best of both worlds.