The Sprint variant will work in most overseas markets without issue. As an international traveler I have yet to find somewhere my phone would not work. Be aware though, with Sprint there is a 90 day "hold" before you can unlock the SIM. This means that you will be carrier locked to Sprint and their roaming partners (which means insane roaming charges).
After the 90 days you can contact the international department and they will complete the request to unlock your phone, shoot you and email advising you to reboot your phone (if it did not automatically reboot) and then you can pop in any international GSM or CDMA/CDMA2000 SIM overseas