Sounds like you are going to buy an iPhone either way, and the worst thing you will have to do if iActivator doesn't work is perform a restore. You should give it a shot and let us all know definitively.
I can tell you that iActivator works well to jailbreak/re-jail the iPhone but that's as far as I have used it.
You might also check the ModMyIphone forums, for potential people who have done what you're asking.