Storage platform looks to add to its 8m individual users and 100,000 businesses.
Sony Ericsson says the promotion will allow Xperia users to stash their digital hordes of photos, music and videos on the Box service.
By logging into a Box account through the app, which can be found in the Android Marketplace, users can enjoy free cloud storage and file sharing for life.
The global offer begins today for anyone with an Xperia X10 smartphone or newer, and runs up until December 31st 2012.
Steve Walker, chief marketing officer, Sony Ericsson, said: "Xperia and Box will provide consumers with access to a massive amount of content on the go putting their smartphone at the very heart of their connected lifestyle."
Presumably, Sony Ericsson's main reason for the partnership is that it will be hoping to see devices fly off shelves for Christmas gifts and during the January sales period.
Aaron Levie, co-founder and CEO of Box, said: "As more people bring their personal devices in to work to take full advantage of mobile computing, it is essential that they never have to worry about storage limitations.
"By partnering with Sony Ericsson we are bringing the full power of Box's cloud content management and sharing to those users."
Box claims more than eight million individuals and 100,000 businesses make use of its services around the world.