I have just tried setting up RTM for Blackberry using GTD principles and discovered exactly the same problem.
The problem is that a "hard" list (a list which is not a smartlist) name maps to a category in BB tasks, but smartlists do not. I started the same way as you, using tags and smartlists for the GTD contexts but it didn't work. So now I have to use hard lists for each context and tags only for projects. I may use the priority field to indicate next actions.
My reasoning is that when looking at my BB the context, @calls, @errands etc is the primary focus. Reviewing by project (tag and smartlist) will have to be done at a computer.
Perhaps the best solution would be a proper RTM app for the BB, instead of struggling with the few fields available in BB tasks.
Posted 5 years ago