(Reuters) - Dead silence. For nearly 20 minutes on the morning of Facebook Inc's trading debut last Friday, the line Nasdaq had opened up to keep traders informed about the social media company's $16 billion IPO had been mute. Well after the stock was supposed to have opened at 11 a.m. New York time, no one from Nasdaq was talking - and there was still no sign of trading. Finally, at 11:28 a.m., an unidentified person announced that the shares would open in about 2 minutes. Nasdaq also said orders and cancellations were still being processed, according to several sources listening to the call. ...