Originally Posted by Brian706
I'm a little confused by your question. An app for extra storage?
You could use any cloud service. Drive, copy, Dropbox, box; all of those offer a free mobile app along with your account.
Also the card reader I linked to will work as well. None of these options require root.
This phone also supports usb on the go I believe without root. Which is similar to the product I linked but less portable and uses usb sticks rather than a micro sd card.
Sorry if I'm misunderstanding the question.
On the linked product page, it says if you're not rooted you'll need to use the card reader with a "3rd party software". I'm not sure what they mean by that. Thanks.