The only countries in the world which use CDMA are the US, Japan, and South Korea (with growing GSM). The rest of the world uses GSM exclusively. So, depending where your travels take you, you may be fine with just the AT&T or T-Mobile varieties (they are identical GSM-only models), or would want the Verizon/Sprint ones which have GSM but also CDMA. The LTE bands on both are identical, and having only GSM will not be a detriment in 99% of the planet. CDMA is a technology which should have been drawn and quartered 20 years ago.