There are a few communities spread in various cities of Italy, quite traditionally a goup of people of the same ethnicity that come together and they created an association. For example, there is a strong presence of Lebanese around Como area, north west of Italy, or a trong presence of Pakistanis the in Brescia area, or Iranian around Milan and so on.
In Rome, a group of people mainly composed by reverts, opened and Islamic Centre called Centro Islamico Imam Mahdi (aj) in 2004, and the centre is still multi-cultural and opened to all enthicities in order to satisfy the needs of all islamic comminities in Italy. For more information about the centre, have a look at their website: http://islamshia.org/
If you would like further information, let me know.
Fi aman Allah