When Samsung first unveiled its new Galaxy S III smartphone, one of the perks presented by the company was the offer of 50GB of free cloud-based storage, available for two years on Dropbox, trumping a similar offer on the HTC One which only gave users 25GB of storage.

Now however, it looks as if Samsung won’t be able to live up to that promise after all, following the apparent decision of US carriers AT&T and Verizon Wireless decision not to play ball.

The revelation first appeared on Dropbox’s support page, where the company stated that Samsung Galaxy S III users on the AT&T and Verizon Wireless networks would not be eligible for the 50GB of free storage offer.  According to Dropbox, carriers have the right to opt out of the offer, and it appears that the US’s two largest carriers have chosen to do so. Dropbox makes no mention of other carriers like T-Mobile or Sprint in its support doc, so it’s fair to assume that those versions of the S III will still come with the offer.

Galaxy S III users in Europe – where the phone has already been launched – are eligible to sign up for 48GB of free storage space. When combined with the free space already offered by Dropbox, this amounts to 66GB of free space for each user.

The majority of users probably won’t be too concerned that the AT&T and Verizon versions of the phone come without the additional storage space, but there could be implications for AT&T users, since the carrier will only offer the 16GB model, having chosen to forgo the 32GB version. Of course, users can always plug in an extra microSD card instead, but they don’t come for free.

AT&T and Verizon haven’t made any statements as to why they have ‘dropped’ the Dropbox offer, although there have been suggestions that the carriers are worried about all the extra data their networks have to carry. Or perhaps, just perhaps, they have their own cloud storage services in the pipeline?