E-Trade is offering its account holders a free application for their BlackBerry smartphones that allows them to get real-time stock information and execute trades on their phones. Now if you’re walking down the street in a big city and see executives throwing themselves out of the windows of some skyscraper, you can read the name on the building, launch your E-Trade account and key in “Sell Mortimer! Sell!”High-end phone users have for a while been able to access E-Trade’s Web site and those of most banks and