Techie
I own the Samsung Galaxy Note 2 smartphone- and besides having a user-replaceable battery, this device also allows the user to pop in a Micro SD card.  More is better, too much is almost enough... and hence the 64-GB model, which permits storing insane numbers of songs on your phone-- in my case, over 7000!  (Three of the songs are great, 2 are OK, and the rest?  Not so good!)  Seriously- this is a 'must own' if your smart phone is not made by Apple!  If you own the iPhone, not so great, there are no user-accessible batteries or Micro SD cards in iPhones.  If you own Android- well, life will be considerably brighter once you pop this in, which took all of like 30 seconds.  You do not need to format it unless you wish to erase what you've already put on it.  Highly recommend - SanDisk is a trusted provider of flash memory devices, and buying from Amazon.com is a no-brainer.