It seems that Frank Vincent, voice actor for Salvatore Leone in GTA3 will be returning in SA according to his website.
"...look forward to Frank lending his voice once again as Don Salvatore Leone in the sequel to Rock Star's Grand Theft Auto III."
Salvatore was the don for the Mafia in GTA3 so could this mean the return of the Mafia in San Andreas? Maybe.
Thanks to GTAGaming for the info.