This might be a repost but I recently installed a new OS on my galaxy s2 and installed Dropbox and was awarded an additional 50gb extra storage. Did a quick search and found this offer but it works on more than just the galaxy s3.
mod amended title per member's assistance. Additional 50GB Dropbox space is free for 2 years only.
i did this but after a while i lost 50GB cos i swapped bak to iphone :(