Install siri on iPhone 4 today is possible with iOS 6.1.1. I found a way to install on devices that it is not allowed by apple. This solution I was surprised, to do this you need to Jailbreak iPhone 4 on iOS 6.1.1 with Evasi0n tool and instal Cydia. If you not Jailbreak go to this link Evasi0n Jailbreak to make this. It possible to install Siri on devices that do not support it, for example to the first generation iPad and iPhone 3GS.
Now step by step I show you how to install Siri on iPhone 4
1) Start Cydia and go into the section Manage> Sources
2) Add a new repository, click on edit and then add and insert
3) After the installation try the tweak Siri for iOS 6.1 and run it
4) When you restart your device let us go back to Cydia and search for the package and run it SiriPort
5) When you restart the device in our home will be a new icon SiriPort , and we enter the " Siri iOS 6 Servers "and then" Download the Certificate "
6) Install the certificate that is proposed
7) After the certificate we start the application again SiriPort and let us go in the Token Fix at this point will open Cydia, install the package Token Fix
8) Reboot the device, we can now proceed with the configuration of the Italian language from the menu Settings> General> Siri by our device.
For some questions please write in comment below. Click here for more info to install siri on iPhone 4