DynDNS has a piece of software called DYNDNS Updater that you load into one of your home systems. It will update the home IP to DYNDNS site hourly or at a regulated interval. Most DSL setups dont have static IP addresses. As such, your IP address can change daily or more or less. The app for the computer resolves that issue and updates the DYNDNS servers of any address changes on your network.
I am using DYNDNS as well but I also loaded the app on one of my home systems and all works perfectly.
Also, you mentioned iPhone. If you go to the appstore and search for Neptune or Aqua Notes, there is a free version of Aquanotes for the iPhone. It works great for monitoring your system from anywhere. You just give it your dyndns address and your done. The web interface is a bit combersome on the iphone.
One last thing. Make sure your router is set up to route port 80 to the IP address of the controller. I ended up setting my Aqua Controller to a static IP as well but did that after I had everything working.
That said, there are 2 things you need to look at:
First, the app that runs on one of your system to update the IP info. If you go to DynDNS and select the support tab, the download will be at the top right corner. It is a must unless your DSL is a Static one which is highly unlikely. You pay extra for that.
Second is the port forwarding in your DSL router. That is how you get to the controller through your firewall from the web. Both are essential and without addressing both, you will not get it working.