Online broker price wars are in season.

E*Trade Financial joined the fray late Friday.

The New York company, best known for its “talking baby” Super Bowl ad and mortgage problems in its banking unit, said that Monday it will charge all customers $9.99 or less per stock and options trade–plus a 75-cent per options contract fee.

Higher-volume traders will continue to pay $7.99 per trade. E*Trade also eliminated annual IRA account fees.

E*Trade says the measure will help it continue “to meet the needs of active traders and long-term investors.”

But the move is clearly a response to price cuts by both Charles Schwab and Fidelity Investments. The entire group is taking a hit from low interest rates and companies can’t say for sure what kind of trading environment they’ll see in 2010.

Price cuts are sure to get investors’ attention, but analysts and executives don’t seem entirely convinced that they’ll bring greater market share or make a big difference.

Such reductions clearly put pressure on commission revenue.

TD Ameritade, the only one of three major online brokerages yet to announce a cut in commissions, says it has no plans to change policy. The company charges a flat $9.99 per trade for all customers.

Earlier this week, Ameritrade CEO Fred Tomczyk says price cuts are a “zero sum game.”

On Tuesday, Fidelity Investments said it would cut and simplify its commissions for online U.S. stock trades to $7.95 a trade, while Schwab last month reduced its online-trading commissions 31% to a flat $8.95 for investors who have small accounts or trade infrequently.

While Ameritrade has yet to respond to the pricing cuts, Schwab says it gets a larger share of assets when it makes such a reduction. So you can be sure that each new gimmick (free ETFs, no account fees, no IRA fees) will draw consideration for new pricing schemes across the industry.