You won't get "internet service" per say.
The Blackberry services plan will open up the necessary channels for the email & BBM to work.
All other functions that require INTERNET will not work.
Not true Mobihand. As Rambo said above, a BB data plan will give you Internet access and access to RIM services such as email, BBM, Facebook, the BB browser, etc. You do not need any other data add on.