As everyone says there is no perfect tool for implementing gtd and they are correct ,it depends upon what you had like.

I am a big patron of technology and don't like paper based system because I personally feel it's difficult to follow , but that's just me.

For blackberry you don't need storm , any blackberry manufactured in last 2 years (8520,8900,9000,9700,bold 2) will do fine, I personally have used todomatrix and I am very very very happy with it, recent version allows syncing with outlook as well ,so if you want outlook tasks , you can use them as well.

i am in the process of teaching my dad how to use it .. would advise you to take demo of it as well.