When I signed in my DropBox with my phone it gave me 48GB free space for 24 months just thought I'd share this information, there is other offers but they give less space:
HTC: 23GB 2 year
Samsung : 48GB 2 year
Dell : 18GB 1 year
HP : 25GB
HTC: 23GB 2 year
Samsung : 48GB 2 year
Dell : 18GB 1 year
HP : 25GB
If you purchased your HP device before October 23, 2015, the 23 GB of bonus space will be available for 6 months from the date of your activation
If you purchased your HP device on or after October 23, 2015, the 23 GB of bonus space will be available for 12 months from the date of your activation