Teathering works well with the blackberry, and there are conflicting reports of the 6gb for 30.00 a month available for the blackberys. I don't know if its an option but you should have a harware upgrade available, and when the blackberry bold comes in a few weeks you will likely have access to the 6gb for 30.00 so data shouldn't be an issue.
As for coverage, being a rogers customer may get sketchy as you chase storms to various areas.
IMO your best bet is to make sure the 300/30 is active on your plan and then budget your data as best you can..
I've used the teathering across most of the country with rogers, it works in most places along major highways short of Northern Ontairo, forget about that place..
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