The only way that would have been effective is if the airline had a video phone. Just calling would only verify a name and would in no way verify that the man holding an ID with that name on it was, in fact, who he claimed to be. Had the agent behaved in a manner that indicated he might be who he said he was, the question might not have ever come up. But he didn't. Who's to say the guy didn't steal the ID? After all, we know that AA pilots had THEIR ID stolen by terrorists in order to gain access to cockpits, what's to stop them from faking the ID of an existing agent?
You dont think the Agent in Charge at the white House would recognize the voice of someone that works for him? If Master Card asks you for your mothers maiden name, last four digits of social security number, zip code, etc. you dont think the Agent in Charge couldnt ask the Agent a series of questions that only he would know the answer to?
Also ever hear of FAX or computers? The pilot wanted American to fax him photos of all known terrorists. Are you saying that within five minutes, the Secret Service couldnt fax or email either the pilot, the gate, the airline, or aiport police a full color photo of the agent.