Although it isn't a new feature, one of Samsung's software perks with the Galaxy S3 is the inclusion of 48 GB of free space in a Dropbox account, an offer that lasts two years. Unfortunately, according to an official Dropbox support page, some U.S. users won't have the option to take advantage of this free space.
AT&T and Verizon have chosen to opt out of this promotion, though their reasoning is unclear. The page does mention these two carriers by name, and makes no mention of the promotion's availability on Sprint or T-Mobile, so there is still a chance that this offer may reach us stateside.
It's possible AT&T and Verizon don't like the idea of users drinking down mobile data with large Dropbox accounts, but it's also within the realm of reason to speculate that AT&T and Verizon are preparing to offer cloud storage solutions of their own, and want to keep the competition away. Whatever the reason, it's probably going to make a lot of people upset.