I got the DNS-321 iTunes server to stream music over a 3G connection to my iPhone.
This is good for anyone who wants to access their media outside of their local home network. For instance if you want to enjoy your music at work but don't want to sync your entire music library to your phone.
I say 3G, but the concept is the same for an Internet connection that is outside of your home network.
1. Set static ip for your NAS. Enable iTunes server on your NAS. Point it to the directory where your media is stored. I made q folder called iTunes_media.
2. Get a DNS hostname.
3. If your router has an auto updated for your DNS hostname. Add your DNS hostname and login info to your router in the ddns section of your router configuration page.
4. Forward port 3689 to the static ip of your NAS.
5. Reset your NAS (you can do it from the configuration user interface)
6. Download a daap (digital audio access protocol I think) client. For the iPhone, search simple daap client in the app store.
7. Launch daap client.
8. For your local network, enter the static ip of your nas into the daap client. Use port 3689.
9. For access outside your network, enter the dns name. Use port 3689.
Enjoy!
I have only tested this for m4a and mp3's. Haven't tried pics or vids. Remember, iTunes server will only "serve" a client file types that it supports.
I have tested this simultaneous access from several users and it works. As long as you don't exceed the upload bandwidth of your Internet gateway, I'm thinking that will be the chokepoint.