There is only one model iPhone sold in three capacities and two colors.
All 4S iPhones are CDMA/GSM. This could have easily been found by looking at the specs on Apples website in less time than it took to type up this posting.
Whether it is factory unlocked or not will depend on where it is being purchased.
Only Apple in China may offer unlocked iPhones, all iPhones sold through authorized carriers are locked and the carriers do not offer unlocking.
Also, keep in mind the warranty is NOT International. Do yourself a favor and wait till you get back to the US to purchase a replacement.