One of the most frequent questions I hear is: "Don't you need a BlackBerry phone for your PlayBook?"
The answer is 'no'. The PlayBook works great with the iPhone 4. My iPhone's WiFi hotspot feature lets me connect to the Internet from my PlayBook virtually anytime I wish. No fumbling. No inconvenience. No buttons to push. The PlayBook finds my phone automatically when other WiFi connections are unavailable. In fact, this automatic connection feature is too good. My PlayBook likes to connect to my phone even when it is asleep!
I have a good data plan, so sharing the phone connection is the way to go. Now my MacBooks, PlayBook and iPhone itself all use the same data plan for the base $30 / month rate.
Now that I think about it, having an iPhone is preferable. It's the geek equivalent of not putting all your technology eggs in one basket. I can use Apple's app eco-system on my phone while I wait for RIM to deliver more native and Android tablet apps. It's good way to handle early adopter impatience.
(Unfortunately RIM rarely mentions compatibility with iPhones or other smart phones. Too bad. Only we geeks will know how good it can be)