It appears that there are only three versions of the iPhone for the entire globe, not just the US. This page lists the networks on which each version can operate, http://www.apple.com/iphone/specs.html

GSM model A1428*:
UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz);
GSM/EDGE (850, 900, 1800, 1900 MHz);
LTE (Bands 4 and 17)

CDMA model A1429*: CDMA EV-DO Rev. A and Rev. B (800, 1900, 2100 MHz);
UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz);
GSM/EDGE (850, 900, 1800, 1900 MHz);
LTE (Bands 1, 3, 5, 13, 25)

GSM model A1429*:
UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz);
GSM/EDGE (850, 900, 1800, 1900 MHz);
LTE (Bands 1, 3, 5) 802.11a/b/g/n Wi-Fi (802.11n 2.4GHz and 5GHz)

Since it only takes the nano sim, I am wondering how quickly nano sims will be available through various carriers in countries around the globe?