OPT process length at Texas Service Center??

OPT expedition

USCIS received by I-765 form on July 28. I am waiting for EAD card now. But my job is going to start on Sept. 6, 2011. I want to expedite my EAD card. Is it the better way to call USCIS and also go to the local USCIS office to talk about the expedition? I need your help how should I approach them and what documents do I need to take.
 
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