The storage comes courtesy of Dropbox, which usually offers 2GB for free with a dropbox account. But due to the partnership with HTC they have upped the storage limit for users who carry an HTC device.
The cloud storage will complement the cloud services offered through HTCSense.com which offers features like backup, security and control over your HTC handset and the HTC Watch, video streaming service.
This offer is open to all Android handsets and not just the new ones. While HTC Windows Phones wont be getting in on this offer, there is nothing to worry about as they already have 25GB through Skydrive.