Sigma 17-70mm F2.8-4 DC Macro
I had this exact same situation with B&H in Aug and Sept (I wonder if they sent the same lenses to you)
I ordered the lens for my A57.
I contacted Sigma about both lenses and the tech service told me that both lens serial numbers were supposedly after the cut-in for the new chip and should work with my camera.
If i sent then lens in Sigma would have looked at it for free (I would have had to pay for shipping), but if I am buying an AF lens new then I expect it to work - not have to send it off to get it working.
So I asked for a refund and eventually found the lens locally for the same price, and it did work straight out of the box.
If you have a local store, they sometimes match other prices (when I first ordered the lens from B&H, my local store didnt have it in stock and I would have had to make a special order, and the price was about $100 + tax more expensive)
Although I didnt end up buying from B&H, my experience with them was positive. They were always helpful and polite when i was dealing with them and they processed the refund very quickly after they received the lens back.
If you are willing to try for a third lens, I would recommend that you ask for one with a serial number starting with 128 (mine does and it works fine) both of the lenses I got from B&H started with 123.
I am very happy with the lens itself - it is on my camera pretty much all the time. If you look in my gallery, pretty much all of the photos from the last 6 months are with that lens.
Good luck with whatever decision you decide to go with