It has been generally agreed upon that Samsung making all of their U.S. Galaxy S III phones nearly identical is a great thing. It is a very rare occurrence when developers from GSM phones and CDMA phones get to work together on development for a single device, and should bring about a lot of development. Despite most of the hardware and software being identical, there are some differences between the variants. The most obvious being the radio, as the four carriers all use different networks to some extent. There could very well be a lot more.
To help future development, XDA Recognized Developer incubus26jc has started a comprehensive list of differences between the devices. The point of the list is to help developers create ROMs and other development that is compatible for all versions of the Galaxy S III.
Thus far, the list is short as developers haven’t had much of a chance to dig into the devices on all four carriers yet. The major differences identified include the radios, model numbers and variations in storage size have been identified. Some solutions have even been discussed, such as using the popular AROMA Installer to let users choose which carrier they’re using, so the ROM knows what to install. As devices get released and developers dig deeper, the list is bound to grow, so any developer interested in developing on the U.S. Galaxy S III should definitely have a look.