First off, it is too close to the June refresh where we can expect iPhone 5, which will almost certainly be multi-carrier. Second, the phone is not even 4G LTE! Finally, as stated earlier, it is not an international GSM phone. Seems best to stick with the BlackBerry for now.
You can expect the next iPhone then. By your reasoning, the current phone should be the iPhone 5 as you seem to think that number necessarily increments with each release. It doesn't.
The next phone may be multi-carrier or it may not. It will have the same capabilities on either network, but there's no data in the wild that says it will necessarily be one chip. Is that you Steve?
4G LTE? True, but for most people that really doesn't matter a lot. Another 6 months of dropped calls or 6 months of good calling with a 6 month delay until you can upgrade to a 4G phone.
It seems best for you to do that. There are plenty of other people, as you can read in the thread, where that does not apply.