Sony Ericsson has been kind enough to roll out the alpha builds of Android 4.0.1 Ice Cream Sandwich ROM (update) for unlocked Xperia handsets. Meant strictly for advanced developers and itchy mobile geeks, the new Android 4.0.1 ICS Alpha ROM can be flashed to unlocked versions of Xperia arc S, Xperia neo V, and Xperia Ray with specific update (4.0.2.A.0.42). With limited features working in the Alpha version of Android 4.0 ICS ROM, it is not recommended for the end consumers. 
In past, Sony Ericsson had faced lot of heat while struggling to roll out the latest updates for its Xperia branded Android family of smartphones. Now, Sony Ericsson is getting pro-active and hence released the Alpha builds of the Android 4.0.1 Ice Cream Sandwich update for select unlocked Xperia devices — Arc S, Neo V and Ray.
The company warns that since the build is still in Alpha stage, several normal features won’t work like calling, Wi-Fi, Bluetooth, FM Radio and ANT+. The Android 4.0 ICS alpha ROM also doesn’t pack the usual pack of Google Mobile Services apps such as Gmail, Google Maps, Google Search and more.
The three handsets would first require to have the bootloader unlocked through Sony Ericsson’s Bootloader unlocking service here. Since you’re unlocking the bootloader, you may not be able to download the final version of Android 4.0 ICS update from Sony Ericsson. 
Interested developers should take a look at the detailed blog post at the Sony Ericsson.