RIM’s touchscreen BlackBerry 9800 may be announced at joint AT&T event next week July 28, 2010 | Devindra Hardawar Last week we reported that RIM’s upcoming new touchscreen Blackberry (which also sports a slide-out keyboard) will likely hit shelves on August 15, according to the BlackBerry Partners Fund’s John Albright. Now Engadget reports that RIM is planning a major joint event with AT&T next Tuesday. It doesn’t take a prophet to read between the lines — it’s very likely that RIM is gearing u