You'll need a working SIM in order to activate it though... I'm just saying this in the case you decide to buy in the aftermarket from someone who was locked, and/or intend to wipe a locked device clean before using it.
Originally Posted by danielbigham
Another way you could go around this is to buy a SIM cutter (it's like two bucks on eBay) and cut your actual SIM so it can work on the iPhone. The SIM cutter will cut a micro SIM out of your SIM, but it will leave the cutout intact, so you'll be able to use it to snap the cut SIM back in and use it back on your Blackberry. Then you could really take the iPhone for a complete ride whenever you want. Of course, it'll need to be unlocked or locked to the same carrier than you.
And then, there's the solution to buy an iPod touch. That'll do the trick, for all intents and purposes, in regard of what you're asking...