As I am little bit familiar with Android devices model numbers, I could use the Samsung Galaxy S3's model numbers pattern here. So, let's tackle each of the Samsung Galaxy S4 model number specifications. These are only some of my initial overview and not yet final until the Samsung Galaxy S4 will finally available this coming April.
International Samsung Galaxy S4 / Galaxy S IV variantsThis is the Samsung Galaxy S4 to be released on these regions - Australia, Europe, New Zealand, Latin America, Africa, Middle East and Asia
Samsung GT-i9500 Galaxy S4 / Galaxy S IVThis device is powered with Samsung Exynos 5 Octa 5410 1.6Ghz, this is already reported to be available for international Europe, Asia, Middle East. There two types of this variant, the 6MB and the 32MB built in memory. This Galaxy S4 variant is a non-LTE and can only be use for GSM/UMTS networks.
Samsung GT-i9502 Galaxy S4 Duos / Galaxy S IVThis is a variant is only for Chinese Market, this is built with dual SIM flexibility. Also powered bySamsung Exynos 5 Octa 5410 but the clock speed is 1.8Ghz.
Samsung GT-i9505 Galaxy S4 LTE / Galaxy S IV LTEThis variant is powered with Qualcomm Snapdragon 600 APQ8064T 1.9Ghz. This is built with LTE capability and will be release in regions where some network provides LTE frequency band.
Samsung SHV-E300L Galaxy S4 LTE / KoreaSpeicific model for Korean market only it also powered with Qualcomm Snapdragon 600 APQ8064T 1.9Ghz and also built with LTE capability.
United States and Canada Samsung Galaxy S4 / Galaxy S IV variantsAll U.S and Canada variants will be powered with Qualcomm Snapdragon 600 APQ8064T 1.9Ghz and already built with dual network capabilities, the primary is for GSM/UMTS and the secondary is for CDMA/LTE. In the United States will be named and coded with different model numbers according to each specific carrier providers such as AT&T, T-Mobile, Sprint, Verizon Wireless, U.S Cellular, Cricket and Metro PCS. When unlocking became illegal in the U.S, then most of this devices are network locked.
This also same goes out in Canada, but mostly only two models will be coded on this region just like the Samsung Galaxy S3 for some network providers that is owned with only one company. Rogers, Bell, Telus, Virgin and Sakstel will be the same, to add - Koodo and Fido as well. Wind, Mobilicity and Videotron will also exactly the same model numbers.
Verizon Samsung SGH-i337 Galaxy S4 LTEThis model number SGH-i337 is sounds so familiar and in-lined with AT&T's Samsung Galaxy S3 which SGH-I747, but the closer to this model number is the Galaxy Note SGH-I317. So, I have a doubt that this will goes to AT&T in the U.S market. This also the same variant goes to Rogers, Bell, Telus, Virgin and Sakstel in Canada. The model number will be added with some letter like 'M' or 'R' so it could be SGH-I317M or SH-i317R.
Samsung SCH-i545 Galaxy S4PDAdb.net already says that this goes for Verizon wireless. This device is capable for GSM, UMTS, CDMA and LTE bands. So, there is nothing to add more here.
T-Mobile and Sprint specific model number were not yet available this time. It could be somewhere from SGH-Txxx for T-Mobile and goes similarly for Wind, Mobilicity and Videotron in Canada with only additional letter. Sprint could be SPH-xxxx.
Those are just an initial overview and not yet final. This may contain errors and can only be proven true when the Samsung Galaxy S4 is available to the public market.