I received 2 GS2's a couple days ago from T-Mobile for my wife and step-daughter (couldn't beat the deal) and they were already loaded with ICS 4.0.4 so I don't know why yours won't be. I use a GS2 that had GB and I upgraded through Kies to 4.0.4
You'll want to upgrade also IMO.
Its easy to do and the phone runs so much smoother.
This is a great forum to get all the info you'll need!