I would have thought that our version would not have it, but,I have found some info here.
http://tinyurl.com/Sigma-17-70-OS-HSM(the f info is incorrect it should be 2,8 to 4)
The information in the site above and in the Sigma literature is quire clear. With Sony or Pentax, use one OR the other. (Some Pentax models do not support the HSM).
Not sure of the consequence of using both but the counter compensation may stress either or both mechanisms. Trial and error would be your best friend.
By the way, does anyone out there have one of these in their grubby paws yet, I really am keen to hear or see some "real people" results.
Concerning the older models, the South African agents approach is to deny the existence of the new model until all his old stock is sold. I am hanging in for the HSM, and slightly better f stop and resolution. Also looking forward to evaluating the respective OS systems.
G