Basically anyone who uses a Box Personal account on an iOS device will get this upgraded free storage space (increased from the usual 5GB of free space usually doled out). According to Box.net's blog post introducing the offer, you'll also get an increased file size upload limit of 100MB instead of 25MB.
It's unfortunate that Android and other mobile users aren't getting this same love, but one of the comments on the blog post suggest a "fix" (we haven't tested this yet):
Download itunes. Make an account. Go to apple store. Download the app on the device. Create account get 50GB space. Go to the phone's settings and scroll down to Store. Click on logout so it logs you out of your itunes account. Also remember to delete the App off the phone.You have 50 days from now to grab your 50GB of free space. What do you think? Will you be using Box.net for your cloud storage now?