The deal with the mutual fund giant resulted in an instant cost savings for Fidelity. But surprisingly, the arrangement also is paying dividends for Lehman in terms of increased trading activity by Fidelity, say people close to the Wall Street investment firm.

Lehman executives, during the firm's most recent earnings call, attributed big gains in equity trading for propelling the firm's second-quarter earnings up 47%. Equity capital markets, which includes equity-trading revenue, rose 85%, and the division is slowly catching up to the fixed income group -- a staple business for Lehman.

Recently, a Lehman Brothers employee, who did not want to be identified, offered some insight into the firm's strategy.

"Some pay for principle trading, others for simple execution. Lehman goes client by client and asks them why they are paying the Street," says the employee. "It's like running a candy store. You figure out why they are coming to the candy store, and you offer them more of it."

Internally, the firm is taking every step it can to quantify how Wall Street pays its trading and research business. In a move to give special treatment to the top paying clients, the firm cut back its printed research reports and put some of its analysts on the trading floor. These analysts are instructed to serve only clients that pay for special treatment. Fidelity, for example, wouldn't be privy to Lehman's stock specialists unless they were willing to cut a bigger check to Lehman for the research part of its services.