It depends if you're getting the phone on a new contract or not.
Because if you're getting the Blackberry that's not on the contract (basically for the full price), you can't use any apps if you don't have the data plan. Even if wi-fi is on, it doesn't let you use them.
But, on the iPhone, if you don't get the data plan, you can use the wi-fi and all of the apps work. So, it just depends on your situation.