No blackberry data plan = no using RIM/blackberry apps that require data service. If you have the plan and then drop it, then you no longer will be able to use those apps.
You may be able to use the hotspot browser to access the internet on wifi without a blackberry data plan, but I don't know. I read mixed information. Some can, some can't, seems to depend on carrier. But even if you can, you still will not be able to use data apps like BBM, push email, etc.