I am hanging back on this one and watching what is happening.  ATT made it crystal clear we could keep our old unlimited data plans and upgrade to new phones.  They never once drew the distinction between domestic and international.  It is always childs play to draw post hoc distinctions, but they weren't there when we relied on them.  I renewed my contract until 2013 based on these assurances.  When Verizon started cancelling people from their equivalent plans who weren't on contract, I called in June and grilled them about this.  They marked up my account.  They marked it up in 2009 as well.  The dictation to Word function that is coming out with the 4s is compelling to me and even had them mark my account last week that if I bought an unlocked 4s at the Apple store in November I could keep my unlimited data plan. I hope they honor their word.  

Since I am going 4 to 4s, this should be a simple SIM swap. At the moment, I'm taking a wait and see attitude.  The unlocked iPhones don't come out for another month.