This, but also be aware that WP has Skydrive integration. I have about 2GB free on my phone (16GB LG Optimus 7), because I have all my music on my phone.
Photos, videos and documents are stored in Skydrive, taking full advantage of those free 25GB, I simply don't need to have those stored locally and available offline on the phone, since I have Wi-Fi pretty much anywhere, and my data plan is more than enough to acess my files when I need them.
Plus, I use the Skydrive apps to have my files permanently synced between my phone and my PC. This way I can delete, add, or edit my stuff on my phone and the changes will also be instantly available on my PC.
If my carrier ever offers an affordable unlimited data plan, I'll even delete the music from the phone. I'll just use Skydrive to store and stream everything. So, consider that the Lumia 900 storage is actually 16+25GB=41GB if you have a decent data plan. (16+7GB=23GB if you don't already have Windows Live account)