how can i install opengl 4.4 on ubuntu 12.04?
Step 1: get an NVIDIA card.
Step 2: download their proprieraty binary driver.
Step 3: install the driver.
There are some important points here. The first one is to clarify a common misunderstanding (that unfortunately seems more prevalent among Linux users): OpenGL isn’t software, and you don’t install it. In order to use a given GL_VERSION, firstly your hardware must support it, and secondly your hardware’s vendor must have a driver available for it. The second one is that NVIDIA is currently the only vendor that offers OpenGL 4.4 support on any of their hardware.
that unfortunately seems more prevalent among Linux users
I will not succumb to zealotry here, but I don’t think this is true - I believe this problem is, just like OpenGL, platform-independent. 
The rest is, of course, valid at present.
I have read at http://www.phoronix.com/scan.php?page=news_item&px=MTUzMTM that lastest OpenGL versions that are supported on Mesa are 3.x versions
=> it does not exist a software implementation of OpenGL that support OpenGL 4.x ???
(if not, how a new driver can to say that it support a 4.x version if doesn’t exist a reference software driver that support 4.x versions, for to can verify that the new driver work exactly as it ?)