Hi guys!
Yesterday I received the Ethernet shield, and wanted to try controlling it from my smartphone browser. Now the question is... How can I set a static IP, so, although I connect it in my home net, I can control it through the Internet? (for example, from work)..
Maybe someone has already asked this question, if so I apologise, I didn't find anything useful...
Thanks a lot! 
Now the question is... How can I set a static IP, so, although I connect it in my home net, I can control it through the Internet?
You can't. The Arduino is connected, generally, to a home network via a router. The router has a forward facing IP address that you would talk to from a device not on your home network. The router then talks to the Arduino on a specific port, using port forwarding. The Arduino uses the IP address assigned by the router (best if it's a static (local) address) and the port that the router will talk to the Arduino on.
Really? What a pitty! =(
Is there no way I can communicate with the Ethernet shield from a device that is not in its same network? 
Is there no way I can communicate with the Ethernet shield from a device that is not in its same network?
Yes, but you don't communicate with it directly. You configure your router to forward some data directly to a specific (local) IP address, and you assign that specific (local) address to the Arduino.
Then, from outside your network, you communicate with your router, and deals with getting the data to/from the correct local address/port (the one that the Arduino is using).
Thank you very much for your answers! The last one, the stop! 
IPAddress ip(192,168,2,2);
right?
Thank you!
I set a static IP using ...right?
Right. Just make sure that the router agrees that that is the Arduino's IP address. Typically, the third digit in a home network is either 0 or 1.