(Smart Money) — As markets went berserk in August volatility, a record number of investors turned to smartphones and tablets to review their holdings and to execute trades.  The ranks of mobile traders are small, but at some brokerages they’re growing faster than the market for smartphones. At TD Ameritrade (AMTD: 14.05, -0.47,-3.24%), mobile usage of its app has more than doubled over the past year, due in part to a major boost in August. ShareBuilder, which introduced mobile investment banking this year, reports four to five million page views from mobile apps each month and that roughly 30,000 investor trades were executed in August, up 63% from July.

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