Since it's already Sunday morning halfway around the world in New Zealand, BBM for iPhone has already dropped for the Kiwis, so you can actually trick the App Store into thinking you're over there, and not wherever you're actually at by changing your region in the App Store's Apple ID settings.
First, you'll need to open the App Store, and scroll all the way down to where you see your Apple ID.
Click on your Apple ID, and then View Apple ID.
Then click Country/Region.
Change the "store" location to New Zealand and click Next. This is where it gets tricky.
Since your credit card won't be accepted in the New Zealand App Store, the secret is to select "None" under Credit Card as shown below.
Next, under the Billing Address you must add a Suburb (use "Jacksonville"), and edit the Postal Code to 6004. Click Done. This information has to be added for it to work.
Your region will now be set to New Zealand! Simply search for "BBM", and it's about the 6th or 7th result to the right. Also, you can click this link to be taken directly to the app download.