(FORTUNE Magazine) – The recent acquisition of AT&T Wireless by Cingular for $41 billion and the news that AT&T is being dropped from the Dow got us thinking about how shareholders benefit--or don't--from Wall Street dealmaking. For perspective, we looked back at the mother of all spinoffs, the 1984 breakup of AT&T and the creation of the Baby Bells. Turns out that a Ma Bell shareholder who held on to the growing portfolio would have gotten a so-so return--8.2% annually, compounded and excluding dividends. The S&P 500, by contrast, has a compound annual return of 10.5% over the same period. Who really profits from all the wheeling and dealing? Consider that Merrill Lynch and Lehman Brothers will reportedly split the bulk of $80 million in fees on the AT&T Wireless deal alone. --Kate Bonamici