May 31, 2011 14:21 GMT  ·  By

Dropbox has been doing great so far, the file-sharing, backup and sync app has been installed by 25 million people and their number is growing each day. It's the best known of the bunch of similar services, but the company is not stopping here, it partnered with Softbank and Sony Ericsson to promote the app with mobile users.

According to Bloomberg, Dropbox has struck a deal with the third-largest carrier in Japan and the phone maker to have Dropbox pre-installed on devices as well as promoted in ads and shown off in stores.

Dropbox is looking to expand further in Europe and Asia. Softbank will be promoting the app in Japan, it will come bundled with a couple of phones and sales staff will be trained to demonstrate it to potential customers.

Sony Ericsson will sell Android phones with Dropbox pre-installed in several countries, the UK and Denmark in Europe but also Australia and Indonesia. The terms of the deals haven't been disclosed.

Dropbox enables users to easily sync files between two computers and other devices as well as back up important work by simply saving it to the Dropbox folder.

The app's simplicity is its main touting point. Dropbox users can also easily share files with colleagues and friends or publicly with the web. It comes with 2 GB by default, for free, though you can get more if you get people to sign up.

In the Softbank deal, users will get 3 GB of free storage. Paid tiers get 50 GB for $9.99 a month or 100 GB for $19.99 a month.

The mobile up though is rather lacking and nowhere near as capable as the desktop one. It enables users to see the files they keep online and download them one at a time. They can also upload new ones. All of this though has to be done manually, eliminating much of the appeal of Dropbox.