Hello guys! I know nothing when it comes to smartphones and their operating systems.
So my question is: can I upgrade manually the operating system of my phone?! For example, I'm willing to buy a Sony Ericsson smartphone (Neo or Arc) and it's coming with Andriod 2.3. But couple of days ago, Google released Andriod 4.0, so can I upgrade it manually or only SE does while manufacturing the devices?
you can upgrade it manually, but I dont know if the phone you are buying is going to be compatible with the new android or if it will be able to handle the load. Try google and search for the specific phone you want and the android version, and if not you could to XDA forums, they are more into the android environment and there are a lot of people who can help with that.
In order to upgrade your device to Android 4.0, the Ram of your device should be of a minimum of 256 Mb and it should have a decent GPU. The SE Neo and Arc can answer these demands easily, so no worries there!
Here's part of an article from http://www.techradar.com/news/mobile-computing/android-4-0-ice-cream-sandwich-everything-you-need-to-know-954464
Android 4.0 Ice Cream Sandwich update
Google has confirmed it is working on an Android 4.0 update for the Samsung Nexus S and other Android devices.

Director of Android operating system User Experience Matias Duarte told Engadget that Google is. "Currently in the process for releasing Ice Cream Sandwich for Nexus S. Theoretically it should work for any 2.3 device."

Motorola confirmed to TechRadar that the Motorola Razr will launch in the UK with Android 2.3, but that there will be an update to 4.0in 2012.
I don't recommend upgrading your device, things could not run as smoothly as before! Either wait for the new phones to be released with the new Android OS or be satisfied with the v2.3!
No upgrades are really recommended,only if the updates are official but if you are gonna root and upgrade to a custom mod then their is a risk (not huge but it still a risk) but with official updates it's a smooth operation and nothing goes wrong,Sony Ericsson announced that they will update all their Xpera 2011 line to the latest android OS 4.0 so if you are getting an xperia phone make sure it was released in 2011.
Thanks guys. I'll check the XDA forums soon. And it seems I'll wait till the next wave of Xperia phones.